anchor.diff:      ++ opt mmsSupport libmms
       ++ opt mpg123Support mpg123
       ++ opt aacSupport faad2
  +    ++ opt lameSupport lame
       ++ opt zipSupport zziplib
       ++ opt (!stdenv.isDarwin && pulseaudioSupport) libpulseaudio
       ++ opt (!stdenv.isDarwin && jackSupport) libjack2
  
positive.code:       (mkFlag mmsSupport "mms")
        (mkFlag mpg123Support "mpg123")
        (mkFlag aacSupport "aac")
        (mkFlag (!stdenv.isDarwin && pulseaudioSupport) "pulse")
        (mkFlag (!stdenv.isDarwin && jackSupport) "jack")
        (mkFlag stdenv.isDarwin "osx")
  
negative.code: , mmsSupport ? true, libmms
  , mpg123Support ? true, mpg123
  , aacSupport ? true, faad2
  , lameSupport ? true, lame
  , pulseaudioSupport ? true, libpulseaudio
  , jackSupport ? true, libjack2
  , gmeSupport ? true, game-music-emu
  