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:   # same package in the (recursive) dependencies of the package being
    # built. Will delay failures, if any, to compile time.
    allowInconsistentDependencies ? false
  , maxBuildCores ? 4 # GHC usually suffers beyond -j4. https://ghc.haskell.org/trac/ghc/ticket/9221
  , # If set to true, this builds a pre-linked .o file for this Haskell library.
    # This can make it slightly faster to load this library into GHCi, but takes
    # extra disk space and compile time.
  
negative.code:     "--package-db=$packageConfDir"
      (optionalString (enableSharedExecutables && stdenv.isLinux) "--ghc-option=-optl=-Wl,-rpath=$out/lib/${ghc.name}/${pname}-${version}")
      (optionalString (enableSharedExecutables && stdenv.isDarwin) "--ghc-option=-optl=-Wl,-headerpad_max_install_names")
      (optionalString enableParallelBuilding "--ghc-options=${parallelBuildingFlags}")
      (optionalString useCpphs "--with-cpphs=${cpphs}/bin/cpphs --ghc-options=-cpp --ghc-options=-pgmP${cpphs}/bin/cpphs --ghc-options=-optP--cpp")
      (enableFeature (enableDeadCodeElimination && !stdenv.hostPlatform.isAarch32 && !stdenv.hostPlatform.isAarch64 && (versionAtLeast "8.0.1" ghc.version)) "split-objs")
      (enableFeature enableLibraryProfiling "library-profiling")
  