anchor.diff: -{ stdenv, lib, fetchurl, fetchpatch, makeWrapper
  +{ stdenv, lib, fetchFromGitHub, fetchpatch, makeWrapper
   , coq, ocamlPackages, coq2html
   , tools ? stdenv.cc
   }:
  
positive.code:   enableParallelBuilding = true;
  
    patchPhase = ''
      substituteInPlace ./VERSION --replace 3.4 3.5
      substituteInPlace ./configure \
        --replace '{toolprefix}gcc' '{toolprefix}cc'
    '';
  
negative.code:   name    = "compcert-${version}";
    version = "3.5";
  
    src = fetchFromGitHub {
      owner = "AbsInt";
      repo = "CompCert";
      rev = "v${version}";
      sha256 = "1g8067a5x3vd0l47d04gjvy5yx49nghh55am5d1fbrjirfsnsz8j";
    };
  
    nativeBuildInputs = [ makeWrapper ];
  