gcc49: Fix build on darwin

pkgs/development/compilers/gcc/4.9/default.nix

@@ -154,7 +154,10 @@ stdenv.mkDerivation ({
 
   hardeningDisable = [ "format" "pie" ];
 
-  outputs = if langJava || langGo then ["out" "man" "info"]
+  # When targetting darwin, libgcc_ext.10.{4,5}.dylib are created as
+  # MH_DYLIB_STUB files, which install_name_tool can't change, so we
+  # get a cycle between $out and $lib.
+  outputs = if langJava || langGo || targetPlatform.isDarwin then ["out" "man" "info"]
     else [ "out" "lib" "man" "info" ];
   setOutputFlags = false;
   NIX_NO_SELF_RPATH = true;
@@ -328,7 +331,6 @@ stdenv.mkDerivation ({
     maintainers = with lib.maintainers; [ veprbl ];
 
     platforms = lib.platforms.unix;
-    badPlatforms = lib.platforms.darwin;
   };
 }
 

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

@@ -6,14 +6,16 @@
 , langGo }:
 
 assert langJava -> lib.versionOlder version "7";
-assert langAda -> gnatboot != null;
-
-lib.optionalString (hostPlatform.isSunOS && hostPlatform.is64bit) ''
+assert langAda -> gnatboot != null; let
+  needsLib
+    =  (lib.versionOlder version "7" && (langJava || langGo))
+    || (lib.versions.major version == "4" && lib.versions.minor version == "9" && targetPlatform.isDarwin);
+in lib.optionalString (hostPlatform.isSunOS && hostPlatform.is64bit) ''
   export NIX_LDFLAGS=`echo $NIX_LDFLAGS | sed -e s~$prefix/lib~$prefix/lib/amd64~g`
   export LDFLAGS_FOR_TARGET="-Wl,-rpath,$prefix/lib/amd64 $LDFLAGS_FOR_TARGET"
   export CXXFLAGS_FOR_TARGET="-Wl,-rpath,$prefix/lib/amd64 $CXXFLAGS_FOR_TARGET"
   export CFLAGS_FOR_TARGET="-Wl,-rpath,$prefix/lib/amd64 $CFLAGS_FOR_TARGET"
-'' + lib.optionalString (lib.versionOlder version "7" && (langJava || langGo)) ''
+'' + lib.optionalString needsLib ''
   export lib=$out;
 '' + lib.optionalString langAda ''
   export PATH=${gnatboot}/bin:$PATH

pkgs/top-level/all-packages.nix

@@ -12812,6 +12812,9 @@ with pkgs;
     isl = if !stdenv.isDarwin then isl_0_11 else null;
 
     cloog = if !stdenv.isDarwin then cloog_0_18_0 else null;
+
+    # Build fails on Darwin with clang
+    stdenv = if stdenv.isDarwin then gccStdenv else stdenv;
   }));
 
   gcc6 = lowPrio (wrapCC (callPackage ../development/compilers/gcc/6 {