anchor.diff: -{ stdenv, fetchgit, fetchurl, cmake, pkgconfig, boost, libunwind, libmemcached
  +{ stdenv, fetchgit, cmake, pkgconfig, boost, libunwind, libmemcached
   , pcre, libevent, gd, curl, libxml2, icu, flex, bison, openssl, zlib, php
   , expat, libcap, oniguruma, libdwarf, libmcrypt, tbb, gperftools, glog, libkrb5
   , bzip2, openldap, readline, libelf, uwimap, binutils, cyrus_sasl, pam, libpng
  
positive.code: 
  stdenv.mkDerivation rec {
    name    = "hhvm-${version}";
    version = "3.21";
  
    # use git version since we need submodules
    src = fetchgit {
      url    = "https://github.com/facebook/hhvm.git";
      rev    = "56483773e2edd9e61782f1901ce40e47959e71b8";
      sha256 = "0dmdk98nv04m0fv6909gfbsxqlkckn369yi7kadhir0r7vxsj7wa";
      fetchSubmodules = true;
    };
  
  
negative.code: 
    patches = [
      ./flexible-array-members-gcc6.patch
    ];
  
    enableParallelBuilding = true;
  