firefox-wayland: Add missing dependency libglvnd (libEGL)

Firefox running in wayland mode is unable to find and load
libEGL.so (and says so on stdout). This puts it in "basic"
mode (unaccelerated graphics) and disables WebGL. Fix this by adding
libglvnd to the LD_LIBRARY_PATH.

pkgs/applications/networking/browsers/firefox/wrapper.nix

@@ -2,7 +2,7 @@
 
 ## various stuff that can be plugged in
 , flashplayer, hal-flash
-, MPlayerPlugin, ffmpeg, xorg, libpulseaudio, libcanberra-gtk2
+, MPlayerPlugin, ffmpeg, xorg, libpulseaudio, libcanberra-gtk2, libglvnd
 , jrePlugin, icedtea_web
 , bluejeans, djview4, adobe-reader
 , google_talk_plugin, fribid, gnome3/*.gnome-shell*/
@@ -77,6 +77,7 @@ let
       libs =   lib.optional stdenv.isLinux udev
             ++ lib.optional ffmpegSupport ffmpeg
             ++ lib.optional gssSupport kerberos
+            ++ lib.optional gdkWayland libglvnd
             ++ lib.optionals (cfg.enableQuakeLive or false)
             (with xorg; [ stdenv.cc libX11 libXxf86dga libXxf86vm libXext libXt alsaLib zlib ])
             ++ lib.optional (enableAdobeFlash && (cfg.enableAdobeFlashDRM or false)) hal-flash