anchor.diff: -{ stdenv, fetchurl, flex, bison, pkgconfig, libdrm, file, expat, makedepend
  +{ stdenv, fetchurl, flex, bison, pkgconfig, intltool, libdrm, file, expat, makedepend
   , libXxf86vm, libXfixes, libXdamage, glproto, dri2proto, libX11, libxcb, libXext
   , libXt, udev, enableTextureFloats ? false, enableR600LlvmCompiler ? false
   , python, libxml2Python, autoconf, automake, libtool, llvm, writeText }:
  
positive.code:     + stdenv.lib.optionalString enableTextureFloats " --enable-texture-float";
  
    buildInputs = [
      autoconf automake libtool expat libxml2Python udev llvm
      libdrm libXxf86vm libXfixes libXdamage glproto dri2proto libX11 libXext libxcb libXt
    ];
  
  
negative.code: else
  
  let
    version = "9.1";
  in
  stdenv.mkDerivation {
    name = "mesa-${version}";
  
    src = fetchurl {
      url = "ftp://ftp.freedesktop.org/pub/mesa/${version}/MesaLib-${version}.tar.bz2";
      sha256="0yvhl0vdg32h0xr4xi348gkp0hlcc16j1cfxn4pyc9pywyzlqj5g";
    };
  
    prePatch = "patchShebangs .";
  