anchor.diff:        --subst-var-by libc_lib ${getLib stdenv.cc.libc}
       substituteInPlace Modules/FindCxxTest.cmake \
         --replace "$""{PYTHON_EXECUTABLE}" ${stdenv.shell}
  -    configureFlags="--parallel=''${NIX_BUILD_CORES:-1} $configureFlags"
  +    # BUILD_CC and BUILD_CXX are used to bootstrap cmake
  +    configureFlags="--parallel=''${NIX_BUILD_CORES:-1} CC=$BUILD_CC CXX=$BUILD_CXX $configureFlags"
     '';
   
     configureFlags = [
  
positive.code:     ++ optional useQt4 qt4
      ++ optional withQt5 qtbase;
  
    propagatedBuildInputs = optional stdenv.isDarwin ps;
  
    preConfigure = ''
  
negative.code: { stdenv, fetchurl, fetchpatch, pkgconfig
  , bzip2, curl, expat, libarchive, xz, zlib, libuv, rhash
  , buildPackages
  # darwin attributes
  , ps
  , isBootstrap ? false
  