anchor.diff:  
     toolchainName = "com.apple.dt.toolchain.XcodeDefault";
     sdkName = "${xcodePlatform}${sdkVer}";
  +  xcrunSdkName = lib.toLower xcodePlatform;
   
     # TODO: expose MACOSX_DEPLOYMENT_TARGET in nix so we can use it here.
     sdkBuildVersion = "17E189";
  
positive.code:   '';
  
    xcrun = writeShellScriptBin "xcrun" ''
  while [ $# -gt 0 ]; do
     case "$1" in
           --sdk | -sdk) shift ;;
  
negative.code:     esac
      shift
  done
  
  if ! [[ -z "$@" ]]; then
     exec "$@"
  fi
  