anchor.diff:      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 $CFLAGS_FOR_TARGET"
  -  '' + stdenv.lib.optionalString stdenv.isDarwin ''
  -    if SDKROOT=$(/usr/bin/xcrun --show-sdk-path); then
  -      configureFlagsArray+=(--with-native-system-header-dir=$SDKROOT/usr/include)
  -      makeFlagsArray+=( \
  -       CFLAGS_FOR_BUILD=-F$SDKROOT/System/Library/Frameworks \
  -       CFLAGS_FOR_TARGET=-F$SDKROOT/System/Library/Frameworks \
  -       FLAGS_FOR_TARGET=-F$SDKROOT/System/Library/Frameworks \
  -      )
  -    fi
     '';
   
     ABSOLUTE_LIBTOOL_EXCLUDED = libPathExcludes;
  
positive.code: { stdenv, fetchurl, noSysDirs
  , langC ? true, langCC ? true, langFortran ? false
  , langObjC ? stdenv.isDarwin
  , langObjCpp ? stdenv.isDarwin
  , langJava ? false
  , langAda ? false
  , langVhdl ? false
  
negative.code: 
  # LTO needs libelf and zlib.
  assert libelf != null -> zlib != null;
  
  # The go frontend is written in c++
  assert langGo -> langCC;
  