treewide: replace libc == "msvcrt" with isMinGW

msvcrt is only one of the libcs in MinGW. We therefore
replace explictly testing for msvcrt with the isMinGW
predicate. This lays the foundation for ucrt64 support.

pkgs/development/compilers/gcc/common/configure-flags.nix

···
   # See https://github.com/NixOS/nixpkgs/pull/209870#issuecomment-1500550903
   disableBootstrap' = disableBootstrap && !langFortran && !langGo;
 
-  crossMingw = targetPlatform != hostPlatform && targetPlatform.libc == "msvcrt";
+  crossMingw = targetPlatform != hostPlatform && targetPlatform.isMinGW;
   crossDarwin = targetPlatform != hostPlatform && targetPlatform.libc == "libSystem";
 
   targetPrefix = lib.optionalString (stdenv.targetPlatform != stdenv.hostPlatform)

pkgs/development/compilers/gcc/common/libgcc.nix

···
   (pkg: pkg.overrideAttrs (previousAttrs:
     lib.optionalAttrs (
       targetPlatform != hostPlatform &&
-      (enableShared || targetPlatform.libc == "msvcrt") &&
+      (enableShared || targetPlatform.isMinGW) &&
       withoutTargetLibc
     ) {
       makeFlags = [ "all-gcc" "all-target-libgcc" ];

pkgs/development/compilers/gcc/default.nix

···
     patches = callFile ./patches {};
 
     /* Cross-gcc settings (build == host != target) */
-    crossMingw = targetPlatform != hostPlatform && targetPlatform.libc == "msvcrt";
+    crossMingw = targetPlatform != hostPlatform && targetPlatform.isMinGW;
     stageNameAddon = if withoutTargetLibc then "stage-static" else "stage-final";
     crossNameAddon = optionalString (targetPlatform != hostPlatform) "${targetPlatform.config}-${stageNameAddon}-";
 

pkgs/development/libraries/boost/generic.nix

···
 , enableDebug ? false
 , enableSingleThreaded ? false
 , enableMultiThreaded ? true
-, enableShared ? !(with stdenv.hostPlatform; isStatic || libc == "msvcrt") # problems for now
+, enableShared ? !(with stdenv.hostPlatform; isStatic || isMinGW) # problems for now
 , enableStatic ? !enableShared
 , enablePython ? false
 , enableNumpy ? false
···
     ++ lib.optional (!enablePython) "--without-python"
     ++ lib.optional needUserConfig "--user-config=user-config.jam"
     ++ lib.optional (stdenv.buildPlatform.isDarwin && stdenv.hostPlatform.isLinux) "pch=off"
-    ++ lib.optionals (stdenv.hostPlatform.libc == "msvcrt") [
+    ++ lib.optionals stdenv.hostPlatform.isMinGW [
     "threadapi=win32"
   ] ++ extraB2Args
   );
···
     # Make boost header paths relative so that they are not runtime dependencies
     cd "$dev" && find include \( -name '*.hpp' -or -name '*.h' -or -name '*.ipp' \) \
       -exec sed '1s/^\xef\xbb\xbf//;1i#line 1 "{}"' -i '{}' \;
-  '' + lib.optionalString (stdenv.hostPlatform.libc == "msvcrt") ''
+  '' + lib.optionalString stdenv.hostPlatform.isMinGW ''
     $RANLIB "$out/lib/"*.a
   '';
 

pkgs/development/libraries/libiconv/default.nix

···
   ];
 
   postPatch =
-    lib.optionalString ((stdenv.hostPlatform != stdenv.buildPlatform && stdenv.hostPlatform.libc == "msvcrt") || stdenv.cc.nativeLibc)
+    lib.optionalString ((stdenv.hostPlatform != stdenv.buildPlatform && stdenv.hostPlatform.isMinGW) || stdenv.cc.nativeLibc)
       ''
         sed '/^_GL_WARN_ON_USE (gets/d' -i srclib/stdio.in.h
       ''

pkgs/development/libraries/libjpeg-turbo/default.nix

···
 
   # This is needed by freeimage
   patches = [ ./0001-Compile-transupp.c-as-part-of-the-library.patch ]
-    ++ lib.optional (stdenv.hostPlatform.libc or null == "msvcrt")
+    ++ lib.optional stdenv.hostPlatform.isMinGW
     ./mingw-boolean.patch;
 
   outputs = [ "bin" "dev" "dev_private" "out" "man" "doc" ];

pkgs/development/libraries/libxml2/default.nix

···
     (stdenv.hostPlatform == stdenv.buildPlatform || stdenv.hostPlatform.isCygwin || stdenv.hostPlatform.isLinux || stdenv.hostPlatform.isWasi)
 , icuSupport ? false
 , icu
-, enableShared ? stdenv.hostPlatform.libc != "msvcrt" && !stdenv.hostPlatform.isStatic
+, enableShared ? !stdenv.hostPlatform.isMinGW && !stdenv.hostPlatform.isStatic
 , enableStatic ? !enableShared
 , gnome
 }:

pkgs/development/libraries/zlib/default.nix

···
   setOutputFlags = false;
   outputDoc = "dev"; # single tiny man3 page
 
-  dontConfigure = stdenv.hostPlatform.libc == "msvcrt";
+  dontConfigure = stdenv.hostPlatform.isMinGW;
 
   preConfigure = lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
     export CHOST=${stdenv.hostPlatform.config}
···
   ''
     # Non-typical naming confuses libtool which then refuses to use zlib's DLL
     # in some cases, e.g. when compiling libpng.
-  + lib.optionalString (stdenv.hostPlatform.libc == "msvcrt" && shared) ''
+  + lib.optionalString (stdenv.hostPlatform.isMinGW && shared) ''
     ln -s zlib1.dll $out/bin/libz.dll
   '';
 
···
   dontStrip = stdenv.hostPlatform != stdenv.buildPlatform && static;
   configurePlatforms = [];
 
-  installFlags = lib.optionals (stdenv.hostPlatform.libc == "msvcrt") [
+  installFlags = lib.optionals stdenv.hostPlatform.isMinGW [
     "BINARY_PATH=$(out)/bin"
     "INCLUDE_PATH=$(dev)/include"
     "LIBRARY_PATH=$(out)/lib"
···
 
   makeFlags = [
     "PREFIX=${stdenv.cc.targetPrefix}"
-  ] ++ lib.optionals (stdenv.hostPlatform.libc == "msvcrt") [
+  ] ++ lib.optionals stdenv.hostPlatform.isMinGW [
     "-f" "win32/Makefile.gcc"
   ] ++ lib.optionals shared [
     # Note that as of writing (zlib 1.2.11), this flag only has an effect

pkgs/top-level/all-packages.nix

···
   # 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 or windows.mingw_w64_headers
+  in     if stdenv.targetPlatform.isMinGW then targetPackages.windows.mingw_w64_headers or windows.mingw_w64_headers
     else if libc == "nblibc" then targetPackages.netbsdCross.headers or netbsdCross.headers
     else if libc == "libSystem" && stdenv.targetPlatform.isAarch64 then targetPackages.darwin.LibsystemCross or darwin.LibsystemCross
     else null;