treewide: Try to make a few bootstrapping things more consistent

- Introduce `preLibcCrossHeaders` to bootstrap libgcc and compiler-rt
the same way.

- Organize LLVM bintools as `bintools{-unwrapped,,NoLibc}` for
consistency with GNU Binutils and Apple's cctools.

- Do Android changes for all `llvmPackages` for consistency.

- Improve the way the default GCC and LLVM versions are selected.

pkgs/development/compilers/llvm/10/compiler-rt/default.nix

···
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "1yjqjri753w0fzmxcyz687nvd97sbc9rsqrxzpq720na47hwh3fr";
+  src = fetch "compiler-rt" "1yjqjri753w0fzmxcyz687nvd97sbc9rsqrxzpq720na47hwh3fr";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
···
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
···
     ./gnu-install-dirs.patch
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
-
 
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
···
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }

pkgs/development/compilers/llvm/10/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 

pkgs/development/compilers/llvm/11/compiler-rt/default.nix

···
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "0x1j8ngf1zj63wlnns9vlibafq48qcm72p4jpaxkmkb4qw0grwfy";
+  src = fetch "compiler-rt" "0x1j8ngf1zj63wlnns9vlibafq48qcm72p4jpaxkmkb4qw0grwfy";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
···
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
···
     ./normalize-var.patch
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
-
 
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
···
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }

pkgs/development/compilers/llvm/11/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 

pkgs/development/compilers/llvm/12/compiler-rt/default.nix

···
 
 in
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation {
   pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "0d444qihq9jhqnfv003cr704v363va72zl6qaw2algj1c85cva45";
···
     ./normalize-var.patch
   ]# ++ lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
     ++ lib.optional stdenv.hostPlatform.isAarch32 ./armv7l.patch;
-
 
   # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
   # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra

pkgs/development/compilers/llvm/12/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
···
     lldClangNoCompilerRtWithLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [ ];
       extraBuildCommands = mkExtraBuildCommands0 cc;
     };
···
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt-libc = callPackage ./compiler-rt ({ inherit llvm_meta; } //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      inherit llvm_meta;
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
 
-    compiler-rt-no-libc = callPackage ./compiler-rt ({ inherit llvm_meta; } //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      inherit llvm_meta;
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
 
     # N.B. condition is safe because without useLLVM both are the same.
     compiler-rt = if stdenv.hostPlatform.isAndroid

pkgs/development/compilers/llvm/7/compiler-rt/default.nix

···
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
 stdenv.mkDerivation {
-  pname = "compiler-rt";
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "1n48p8gjarihkws0i2bay5w9bdwyxyxxbpwyng7ba58jb30dlyq5";
 
···
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
···
   postInstall = lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
     ln -s "$out/lib"/*/* "$out/lib"
   '' + lib.optionalString (useLLVM) ''
-    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/linux/crtbegin.o
-    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/linux/crtend.o
-    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/linux/crtbeginS.o
-    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/linux/crtendS.o
+    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
+    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
+    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
+    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }

pkgs/development/compilers/llvm/7/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt {
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
       stdenv = if stdenv.hostPlatform.useLLVM or false
                then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
                else stdenv;
     };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 

pkgs/development/compilers/llvm/8/compiler-rt/default.nix

···
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
 stdenv.mkDerivation {
-  pname = "compiler-rt";
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
   src = fetch "compiler-rt" "0dqqf8f930l8gag4d9qjgn1n0pj0nbv2anviqqhdi1rkhas8z0hi";
 
···
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [
···
     ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
     ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
   '';
-
 }

pkgs/development/compilers/llvm/8/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 

pkgs/development/compilers/llvm/9/compiler-rt/default.nix

···
 
   useLLVM = stdenv.hostPlatform.useLLVM or false;
   bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  haveLibc = stdenv.cc.libc != null;
   inherit (stdenv.hostPlatform) isMusl;
 
 in
 
-stdenv.mkDerivation rec {
-  pname = "compiler-rt";
+stdenv.mkDerivation {
+  pname = "compiler-rt" + lib.optionalString (haveLibc) "-libc";
   inherit version;
-  src = fetch pname "0xwh79g3zggdabxgnd0bphry75asm1qz7mv3hcqihqwqr6aspgy2";
+  src = fetch "compiler-rt" "0xwh79g3zggdabxgnd0bphry75asm1qz7mv3hcqihqwqr6aspgy2";
 
   nativeBuildInputs = [ cmake python3 llvm.dev ];
   buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
···
     "-DCOMPILER_RT_BUILD_XRAY=OFF"
     "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
     "-DCOMPILER_RT_BUILD_PROFILE=OFF"
-  ] ++ lib.optionals (useLLVM || bareMetal) [
+  ] ++ lib.optionals ((useLLVM || bareMetal) && !haveLibc) [
     "-DCMAKE_C_COMPILER_WORKS=ON"
     "-DCMAKE_CXX_COMPILER_WORKS=ON"
     "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
     "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ lib.optionals (useLLVM && !haveLibc) [
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
   ] ++ lib.optionals (useLLVM) [
     "-DCOMPILER_RT_BUILD_BUILTINS=ON"
-    "-DCMAKE_C_FLAGS=-nodefaultlibs"
     #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
     "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
   ] ++ lib.optionals (bareMetal) [

pkgs/development/compilers/llvm/9/default.nix

···
-{ lowPrio, newScope, pkgs, lib, stdenv, cmake, gccForLibs
+{ lowPrio, newScope, pkgs, lib, stdenv, cmake
+, gccForLibs, preLibcCrossHeaders
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
···
     # doesn’t support like LLVM. Probably we should move to some other
     # file.
 
-    bintools = callPackage ./bintools.nix {};
+    bintools-unwrapped = callPackage ./bintools {};
+
+    bintoolsNoLibc = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+      libc = preLibcCrossHeaders;
+    };
+
+    bintools = wrapBintoolsWith {
+      bintools = tools.bintools-unwrapped;
+    };
 
     lldClang = wrapCCWith rec {
       cc = tools.clang-unwrapped;
···
         echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
       '' + lib.optionalString (!stdenv.targetPlatform.isWasm) ''
         echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + lib.optionalString (stdenv.targetPlatform.isAndroid && stdenv.targetPlatform.useLLVM) ''
+        echo "-lunwind" >> $out/nix-support/cc-ldflags
       '' + lib.optionalString stdenv.targetPlatform.isWasm ''
         echo "-fno-exceptions" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands cc;
···
     lldClangNoLibcxx = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-      };
+      inherit (tools) bintools;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoLibc = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [
         targetLlvmLibraries.compiler-rt
       ];
···
     lldClangNoCompilerRt = wrapCCWith rec {
       cc = tools.clang-unwrapped;
       libcxx = null;
-      bintools = wrapBintoolsWith {
-        inherit (tools) bintools;
-        libc = null;
-      };
+      bintools = tools.bintoolsNoLibc;
       extraPackages = [ ];
       extraBuildCommands = ''
         echo "-nostartfiles" >> $out/nix-support/cc-cflags
       '' + mkExtraBuildCommands0 cc;
     };
 
+    lldClangNoCompilerRtWithLibc = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      inherit (tools) bintools;
+      extraPackages = [ ];
+      extraBuildCommands = mkExtraBuildCommands0 cc;
+    };
+
   });
 
   libraries = lib.makeExtensible (libraries: let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt ({} //
-      (lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
-        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
-      }));
+    compiler-rt-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRtWithLibc
+               else stdenv;
+    };
+
+    compiler-rt-no-libc = callPackage ./compiler-rt {
+      stdenv = if stdenv.hostPlatform.useLLVM or false
+               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
+               else stdenv;
+    };
+
+    # N.B. condition is safe because without useLLVM both are the same.
+    compiler-rt = if stdenv.hostPlatform.isAndroid
+      then libraries.compiler-rt-libc
+      else libraries.compiler-rt-no-libc;
 
     stdenv = overrideCC stdenv buildLlvmTools.clang;
 

pkgs/top-level/all-packages.nix

···
   gerbil-support = callPackage ../development/compilers/gerbil/gerbil-support.nix { };
   gerbilPackages-unstable = gerbil-support.gerbilPackages-unstable; # NB: don't recurseIntoAttrs for (unstable!) libraries
 
-  gccFun = callPackage (if (with stdenv.targetPlatform; isVc4 || libc == "relibc")
-    then ../development/compilers/gcc/6
-    else ../development/compilers/gcc/10);
-  gcc = if (with stdenv.targetPlatform; isVc4 || libc == "relibc")
-    then gcc6 else
-      # aarch64-darwin doesn't support earlier gcc
-      if (stdenv.targetPlatform.isAarch64 && stdenv.isDarwin) then gcc11
-      else if stdenv.targetPlatform.isAarch64 then gcc9 else gcc10;
+  inherit (let
+      num =
+        if (with stdenv.targetPlatform; isVc4 || libc == "relibc") then 6
+        else if (stdenv.targetPlatform.isAarch64 && stdenv.isDarwin) then 11
+        else if stdenv.targetPlatform.isAarch64 then 9
+        else 10;
+      numS = toString num;
+    in {
+      gcc = pkgs.${"gcc${numS}"};
+      gccFun = callPackage (../development/compilers/gcc + "/${numS}");
+    }) gcc gccFun;
   gcc-unwrapped = gcc.cc;
 
   wrapNonDeterministicGcc = stdenv: ccWrapper:
···
 
   crossLibcStdenv =
     if stdenv.hostPlatform.useLLVM or false
-    then overrideCC stdenv buildPackages.llvmPackages_8.lldClangNoLibc
+    then overrideCC stdenv buildPackages.llvmPackages.lldClangNoLibc
     else gccCrossLibcStdenv;
 
   # The GCC used to build libc for the target platform. Normal gccs will be
···
   llvm_6  = llvmPackages_6.llvm;
   llvm_5  = llvmPackages_5.llvm;
 
-  llvmPackages = with targetPlatform;
-    if isDarwin then
-      llvmPackages_7
-    else if isFreeBSD then
-      llvmPackages_7
-    else if isAndroid then
-      llvmPackages_12
-    else if isLinux then
-      llvmPackages_7
-    else if isWasm then
-      llvmPackages_8
-    else
-      llvmPackages_latest;
+  llvmPackages = let
+    choose = platform:
+      /**/ if platform.isDarwin then "7"
+      else if platform.isFreeBSD then "7"
+      else if platform.isAndroid then "12"
+      else if platform.isLinux then "7"
+      else if platform.isWasm then "8"
+      else "latest";
+    minSupported = lib.min (choose stdenv.hostPlatform) (choose stdenv.targetPlatform);
+  in pkgs.${"llvmPackages_${minSupported}"};
 
   llvmPackages_5 = recurseIntoAttrs (callPackage ../development/compilers/llvm/5 {
     inherit (stdenvAdapters) overrideCC;
···
   });
   binutilsNoLibc = wrapBintoolsWith {
     bintools = binutils-unwrapped;
-    libc =
-      /**/ if stdenv.targetPlatform.libc == "msvcrt" then targetPackages.windows.mingw_w64_headers
-      else if stdenv.targetPlatform.libc == "libSystem" then darwin.xcode
-      else if stdenv.targetPlatform.libc == "nblibc" then targetPackages.netbsdCross.headers
-      else null;
+    libc = preLibcCrossHeaders;
   };
 
   bison = callPackage ../development/tools/parsing/bison { };
···
     stdenv = crossLibcStdenv;
   };
 
+  # These are used when buiding compiler-rt / libgcc, prior to building libc.
+  preLibcCrossHeaders = let
+    inherit (stdenv.targetPlatform) libc;
+  in     if libc == "msvcrt" then targetPackages.windows.mingw_w64_headers
+    else if libc == "nblibc" then targetPackages.netbsdCross.headers
+    else null;
+
   # We can choose:
   libcCrossChooser = name:
     # libc is hackily often used from the previous stage. This `or`
···
     else if name == "newlib" then targetPackages.newlibCross or newlibCross
     else if name == "musl" then targetPackages.muslCross or muslCross
     else if name == "msvcrt" then targetPackages.windows.mingw_w64 or windows.mingw_w64
-    else if stdenv.targetPlatform.useiOSPrebuilt then targetPackages.darwin.iosSdkPkgs.libraries or darwin.iosSdkPkgs.libraries
-    else if name == "libSystem" then targetPackages.darwin.xcode
+    else if name == "libSystem" then
+      if stdenv.targetPlatform.useiOSPrebuilt
+      then targetPackages.darwin.iosSdkPkgs.libraries or darwin.iosSdkPkgs.libraries
+      else throw "don't yet have a `targetPackages.darwin.LibsystemCross`"
     else if name == "nblibc" then targetPackages.netbsdCross.libc or netbsdCross.libc
     else if name == "wasilibc" then targetPackages.wasilibc or wasilibc
     else if name == "relibc" then targetPackages.relibc or relibc

pkgs/top-level/darwin-packages.nix

···
 , buildPackages, pkgs, targetPackages
 , pkgsBuildBuild, pkgsBuildHost, pkgsBuildTarget, pkgsHostHost, pkgsTargetTarget
 , stdenv, splicePackages, newScope
+, preLibcCrossHeaders
 }:
 
 let
···
   };
 
   binutilsNoLibc = pkgs.wrapBintoolsWith {
-    libc = null;
+    libc = preLibcCrossHeaders;
     bintools = self.binutils-unwrapped;
   };