anchor.diff:  
     NIX_LDFLAGS = with stdenv.lib;
          optional  fontconfigSupport "-lfontconfig"
  +    ++ optional  fribidiSupport "-lfribidi"
       ++ optionals x11Support [ "-lX11" "-lXext" ]
       ;
   
  
positive.code:       ${if pulseSupport then "--enable-pulse" else "--disable-pulse"}
        ${optionalString (useUnfreeCodecs && codecs != null) "--codecsdir=${codecs}"}
        ${optionalString (stdenv.isi686 || stdenv.isx86_64) "--enable-runtime-cpudetection"}
        --disable-xanim
        --disable-ivtv
        --disable-xvid --disable-xvid-lavc
  
negative.code: { stdenv, fetchurl, pkgconfig, freetype, yasm
  , fontconfigSupport ? true, fontconfig ? null, freefont_ttf ? null
  , fribidiSupport ? true, fribidi ? null
  , x11Support ? true, libX11 ? null, libXext ? null, mesa ? null
  , xineramaSupport ? true, libXinerama ? null
  , xvSupport ? true, libXv ? null
  