libgtk3: mark wayland support as broken

As discussed on the list it requires a matching XDG runtime API level
which is currently not the case (wayland/weston newer than libgtk3 at
the moment). It doesn't normall exhibit build failures, but it fails at
runtime regardless.

Also fixes:
http://autobuild.buildroot.net/results/aae/aae4266c16189b295cc7ceb60000c504ebb60752/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>