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