anchor.diff:  
     enableParallelBuilding = true;
   
  +  passthru = stdenv.lib.optionalAttrs stdenv.isLinux {
  +    inherit gcc;
  +  };
  +
     meta = {
       description = "A c, c++, objective-c, and objective-c++ frontend for the llvm compiler";
       homepage    = http://llvm.org/;
  
positive.code: { stdenv, fetch, cmake, libxml2, libedit, llvm, version, clang-tools-extra_src }:
  
  stdenv.mkDerivation {
    name = "clang-${version}";
  
    unpackPhase = ''
  
negative.code:     "-DCMAKE_BUILD_TYPE=Release"
      "-DCMAKE_CXX_FLAGS=-std=c++11"
    ] ++
    # Maybe with compiler-rt this won't be needed?
    (stdenv.lib.optional stdenv.isLinux "-DGCC_INSTALL_PREFIX=${gcc}") ++
    (stdenv.lib.optional (stdenv.cc.libc != null) "-DC_INCLUDE_DIRS=${stdenv.cc.libc}/include");
  
    patches = [ ./clang-purity.patch ./clang-exports.patch ];
  