anchor.diff:      ++ optionals spiceSupport [ spice-protocol spice ]
       ++ optionals usbredirSupport [ usbredir ]
       ++ optionals stdenv.isLinux [ alsaLib libaio libcap_ng libcap attr ]
  -    ++ optionals xenSupport [ xen ];
  +    ++ optionals xenSupport [ xen ]
  +    ++ optionals openGLSupport [ mesa_noglu epoxy libdrm ];
   
     enableParallelBuilding = true;
   
  
positive.code:     ++ optional hostCpuOnly "--target-list=${hostCpuTargets}"
      ++ optional stdenv.isDarwin "--enable-cocoa"
      ++ optional stdenv.isLinux "--enable-linux-aio"
      ++ optional xenSupport "--enable-xen";
  
    postFixup =
      ''
  
negative.code: , spiceSupport ? !stdenv.isDarwin, spice, spice-protocol
  , usbredirSupport ? spiceSupport, usbredir
  , xenSupport ? false, xen
  , openGLSupport ? true, mesa_noglu, epoxy, libdrm
  , hostCpuOnly ? false
  , nixosTestRunner ? false
  }:
  