anchor.diff:  
     setupCompileFlags = [
       (optionalString (!coreSetup) "-${nativePackageDbFlag}=$setupPackageConfDir")
  -    (optionalString (isGhcjs || isHaLVM || versionOlder "7.8" ghc.version) "-j$NIX_BUILD_CORES")
  -    # https://github.com/haskell/cabal/issues/2398
  -    (optionalString (versionOlder "7.10" ghc.version && !isHaLVM) "-threaded")
  +    (optionalString enableParallelBuilding (parallelBuildingFlags))
  +    "-threaded"       # https://github.com/haskell/cabal/issues/2398
  +    "-rtsopts"        # allow us to pass RTS flags to the generated Setup executable
     ];
   
     isHaskellPkg = x: x ? isHaskellLibrary;
  
positive.code:     (optionalString enableHsc2hsViaAsm "--hsc2hs-option=--via-asm")
    ];
  
    crossCabalFlagsString =
      stdenv.lib.optionalString isCross (" " + stdenv.lib.concatStringsSep " " crossCabalFlags);
  
  
negative.code: , isExecutable ? false, isLibrary ? !isExecutable
  , jailbreak ? false
  , license
    # aarch64 sometimes crashes for -jn with n>1: https://ghc.haskell.org/trac/ghc/ticket/15449
  , enableParallelBuilding ? !stdenv.buildPlatform.isAarch64
  , maintainers ? []
  , doCoverage ? false
  , doHaddock ? !(ghc.isHaLVM or false)
  