icu: Fix cross-building.

The icu4c cross-build process requires access to a full buildRoot of a
native build, so we add a variant of the build that just does the
buildPhase and copies the buildRoot to $out for access by the cross
compile.

pkgs/development/libraries/icu/base.nix

···
 { version, sha256, patches ? [], patchFlags ? "" }:
-{ stdenv, fetchurl, fetchpatch, fixDarwinDylibNames }:
+{ stdenv, fetchurl, fetchpatch, fixDarwinDylibNames
+  # Cross-compiled icu4c requires a build-root of a native compile
+, buildRootOnly ? false, nativeBuildRoot, buildPlatform, hostPlatform
+}:
 
 let
   pname = "icu4c";
-in
-stdenv.mkDerivation {
-  name = pname + "-" + version;
 
-  src = fetchurl {
-    url = "http://download.icu-project.org/files/${pname}/${version}/${pname}-"
-      + (stdenv.lib.replaceChars ["."] ["_"] version) + "-src.tgz";
-    inherit sha256;
-  };
+  baseAttrs = {
+    src = fetchurl {
+      url = "http://download.icu-project.org/files/${pname}/${version}/${pname}-"
+        + (stdenv.lib.replaceChars ["."] ["_"] version) + "-src.tgz";
+      inherit sha256;
+    };
+
+    postUnpack = ''
+      sourceRoot=''${sourceRoot}/source
+      echo Source root reset to ''${sourceRoot}
+    '';
+
+    # https://sourceware.org/glibc/wiki/Release/2.26#Removal_of_.27xlocale.h.27
+    postPatch = if (stdenv.hostPlatform.libc == "glibc" || stdenv.hostPlatform.libc == "musl")
+      then "substituteInPlace i18n/digitlst.cpp --replace '<xlocale.h>' '<locale.h>'"
+      else null; # won't find locale_t on darwin
+
+    inherit patchFlags patches;
+
+    preConfigure = ''
+      sed -i -e "s|/bin/sh|${stdenv.shell}|" configure
 
-  outputs = [ "out" "dev" ];
-  outputBin = "dev";
+      # $(includedir) is different from $(prefix)/include due to multiple outputs
+      sed -i -e 's|^\(CPPFLAGS = .*\) -I\$(prefix)/include|\1 -I$(includedir)|' config/Makefile.inc.in
+    '' + stdenv.lib.optionalString stdenv.isArm ''
+      # From https://archlinuxarm.org/packages/armv7h/icu/files/icudata-stdlibs.patch
+      sed -e 's/LDFLAGSICUDT=-nodefaultlibs -nostdlib/LDFLAGSICUDT=/' -i config/mh-linux
+    '';
 
-  # FIXME: This fixes dylib references in the dylibs themselves, but
-  # not in the programs in $out/bin.
-  buildInputs = stdenv.lib.optional stdenv.isDarwin fixDarwinDylibNames;
+    configureFlags = "--disable-debug" +
+      stdenv.lib.optionalString (stdenv.isFreeBSD || stdenv.isDarwin) " --enable-rpath" +
+      stdenv.lib.optionalString (buildPlatform != hostPlatform) " --with-cross-build=${nativeBuildRoot}";
 
-  postUnpack = ''
-    sourceRoot=''${sourceRoot}/source
-    echo Source root reset to ''${sourceRoot}
-  '';
+    enableParallelBuilding = true;
 
-  # https://sourceware.org/glibc/wiki/Release/2.26#Removal_of_.27xlocale.h.27
-  postPatch = if (stdenv.hostPlatform.libc == "glibc" || stdenv.hostPlatform.libc == "musl")
-    then "substituteInPlace i18n/digitlst.cpp --replace '<xlocale.h>' '<locale.h>'"
-    else null; # won't find locale_t on darwin
+    meta = with stdenv.lib; {
+      description = "Unicode and globalization support library";
+      homepage = http://site.icu-project.org/;
+      maintainers = with maintainers; [ raskin ];
+      platforms = platforms.all;
+    };
+  };
 
-  inherit patchFlags patches;
+  realAttrs = baseAttrs // {
+    name = pname + "-" + version;
 
-  preConfigure = ''
-    sed -i -e "s|/bin/sh|${stdenv.shell}|" configure
+    outputs = [ "out" "dev" ];
+    outputBin = "dev";
 
-    # $(includedir) is different from $(prefix)/include due to multiple outputs
-    sed -i -e 's|^\(CPPFLAGS = .*\) -I\$(prefix)/include|\1 -I$(includedir)|' config/Makefile.inc.in
-  '' + stdenv.lib.optionalString stdenv.isArm ''
-    # From https://archlinuxarm.org/packages/armv7h/icu/files/icudata-stdlibs.patch
-    sed -e 's/LDFLAGSICUDT=-nodefaultlibs -nostdlib/LDFLAGSICUDT=/' -i config/mh-linux
-  '';
+    # FIXME: This fixes dylib references in the dylibs themselves, but
+    # not in the programs in $out/bin.
+    buildInputs = stdenv.lib.optional stdenv.isDarwin fixDarwinDylibNames;
 
-  configureFlags = "--disable-debug" +
-    stdenv.lib.optionalString (stdenv.isFreeBSD || stdenv.isDarwin) " --enable-rpath";
+    # remove dependency on bootstrap-tools in early stdenv build
+    postInstall = stdenv.lib.optionalString stdenv.isDarwin ''
+      sed -i 's/INSTALL_CMD=.*install/INSTALL_CMD=install/' $out/lib/icu/${version}/pkgdata.inc
+    '' + ''
+      substituteInPlace "$dev/bin/icu-config" \
+        --replace \''${pkglibdir}/Makefile.inc "$dev/lib/icu/Makefile.inc"
+    '';
 
-  # remove dependency on bootstrap-tools in early stdenv build
-  postInstall = stdenv.lib.optionalString stdenv.isDarwin ''
-    sed -i 's/INSTALL_CMD=.*install/INSTALL_CMD=install/' $out/lib/icu/${version}/pkgdata.inc
-  '' + ''
-    substituteInPlace "$dev/bin/icu-config" \
-      --replace \''${pkglibdir}/Makefile.inc "$dev/lib/icu/Makefile.inc"
-  '';
+    postFixup = ''moveToOutput lib/icu "$dev" '';
+  };
 
-  postFixup = ''moveToOutput lib/icu "$dev" '';
+  buildRootOnlyAttrs = baseAttrs // {
+    name = pname + "-build-root-" + version;
 
-  enableParallelBuilding = true;
+    preConfigure = baseAttrs.preConfigure + ''
+      mkdir build
+      cd build
+      configureScript=../configure
+    '';
 
-  meta = with stdenv.lib; {
-    description = "Unicode and globalization support library";
-    homepage = http://site.icu-project.org/;
-    maintainers = with maintainers; [ raskin ];
-    platforms = platforms.all;
+    postBuild = ''
+      cd ..
+      mv build $out
+      echo "Doing build-root only, exiting now" >&2
+      exit 0
+    '';
   };
-}
+
+  attrs = if buildRootOnly
+            then buildRootOnlyAttrs
+          else realAttrs;
+in
+stdenv.mkDerivation attrs

pkgs/top-level/all-packages.nix

···
 
   hyena = callPackage ../development/libraries/hyena { };
 
-  icu58 = callPackage ../development/libraries/icu/58.nix
+  icu58 = callPackage ../development/libraries/icu/58.nix {
+    nativeBuildRoot = buildPackages.icu58.override { buildRootOnly = true; };
+  } //
     (stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
       stdenv = overrideCC stdenv gcc6; # with gcc-7: undefined reference to `__divmoddi4'
     });
-  icu59 = callPackage ../development/libraries/icu/59.nix
-    (stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
+  icu59 = callPackage ../development/libraries/icu/59.nix {
+    nativeBuildRoot = buildPackages.icu59.override { buildRootOnly = true; };
+  } // (stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
       stdenv = overrideCC stdenv gcc6; # with gcc-7: undefined reference to `__divmoddi4'
     });
-  icu60 = callPackage ../development/libraries/icu/60.nix
-    (stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
+  icu60 = callPackage ../development/libraries/icu/60.nix {
+    nativeBuildRoot = buildPackages.icu60.override { buildRootOnly = true; };
+  } // (stdenv.lib.optionalAttrs (stdenv.cc.isGNU && stdenv.hostPlatform.isi686) {
       stdenv = overrideCC stdenv gcc6; # with gcc-7: undefined reference to `__divmoddi4'
     });