anchor.diff:  assert bluraySupport      -> available libbluray;
   assert speexSupport       -> available speex;
   assert theoraSupport      -> available libtheora;
  +assert openalSupport      -> available openalSoft;
   assert pulseSupport       -> available libpulseaudio;
   assert bs2bSupport        -> available libbs2b;
   assert cacaSupport        -> available libcaca;
  
positive.code:     ++ optional vdpauSupport       libvdpau
      ++ optional speexSupport       speex
      ++ optional bs2bSupport        libbs2b
      ++ optional libpngSupport      libpng
      ++ optional youtubeSupport     youtube-dl
      ++ optional sdl2Support        SDL2
  
negative.code:     (enableFeature archiveSupport "libarchive")
      (enableFeature dvdreadSupport "dvdread")
      (enableFeature dvdnavSupport "dvdnav")
      (enableFeature openalSupport "openal")
      (enableFeature vaapiSupport "vaapi")
      (enableFeature waylandSupport "wayland")
      (enableFeature stdenv.isLinux "dvbin")
  