anchor.diff:  , libxml2
   , python
   , libusb1
  -, avahi
  +, avahiSupport ? true, avahi
   , libaio
   , runtimeShell
   , lib
  
positive.code:     # the linux-like directory structure is used for proper output splitting
      "-DOSX_PACKAGE=off"
      "-DOSX_FRAMEWORK=off"
    ];
  
    postPatch = ''
  
negative.code:     python
      libxml2
      libusb1
    ] ++ lib.optional python.isPy3k python.pkgs.setuptools
      ++ lib.optional avahiSupport avahi
      ++ lib.optional stdenv.isLinux libaio
      ++ lib.optionals stdenv.isDarwin [ CFNetwork CoreServices ];
  
  