anchor.diff:      ++ (lib.optional enableGui wrapQtAppsHook);
     buildInputs
        = [ boostPython python3 eigen ]
  -    ++ (lib.optional enableGui qtbase);
  +    ++ (lib.optional enableGui qtbase)
  +    ++ (lib.optional stdenv.cc.isClang llvmPackages.openmp);
   
     enableParallelBuilding = true;
     cmakeFlags =
  
positive.code: in
  with stdenv; mkDerivation rec {
    pname = "nextpnr";
    version = "2019.08.21";
  
    src = fetchFromGitHub {
      owner  = "yosyshq";
      repo   = "nextpnr";
      rev    = "c192ba261d77ad7f0a744fb90b01e4a5b63938c4";
      sha256 = "0g2ar1z89b31qw5vgqj2rrcv9rzncs94184dgcsrz19p866654mf";
    };
  
    nativeBuildInputs
  
negative.code: { stdenv, fetchFromGitHub, cmake
  , boost, python3, eigen
  , icestorm, trellis
  , llvmPackages
  
  , enableGui ? true
  , wrapQtAppsHook
  