anchor.diff:  , libdrm
   , libva
   , libvpx
  +, libx11
  +, libxrandr
  +, libxrender
   , mesa
  +, renderproto
   , systemd_lib
   , wayland
   , xorg
  
positive.code:     "--disable-examples"
      "--enable-encoders"
      "--${boolEn (libdrm != null)}-drm"
      "--${boolEn (xorg != null)}-x11"
      "--${boolEn (xorg != null && mesa != null)}-glx"
      "--${boolEn (wayland != null)}-wayland"
      "--${boolEn (wayland != null && mesa != null)}-egl"
      "--disable-gtk-doc"
  
negative.code:     libdrm
      libva
      libvpx
      libx11
      libxrandr
      libxrender
      mesa
      renderproto
      systemd_lib
      wayland
    ];
  
    configureFlags = [
  