anchor.diff:  , aacSupport ? true, faad2 ? null
   , opusSupport ? true, opusfile ? null
   , wavpackSupport ? false, wavpack ? null
  -, ffmpegSupport ? false, ffmpeg_3 ? null
  +, ffmpegSupport ? false, ffmpeg ? null
   , apeSupport ? true, yasm ? null
   # misc plugins
   , zipSupport ? true, libzip ? null
  
positive.code:     ++ optional aacSupport faad2
      ++ optional opusSupport opusfile
      ++ optional zipSupport libzip
      ++ optional ffmpegSupport ffmpeg_3
      ++ optional apeSupport yasm
      ++ optional artworkSupport imlib2
      ++ optional hotkeysSupport libX11
  
negative.code: assert aacSupport -> faad2 != null;
  assert opusSupport -> opusfile != null;
  assert zipSupport -> libzip != null;
  assert ffmpegSupport -> ffmpeg != null;
  assert apeSupport -> yasm != null;
  assert artworkSupport -> imlib2 != null;
  assert hotkeysSupport -> libX11 != null;
  