wayland-compositor: Don't use Wayland types in public API

The definition of wl_display differs between Wayland clients and
servers, and it's unsafe to include both wayland-client.h and
wayland-server.h at the same time.  Fudge around this by making the
compositor public API use void * rather than struct wl_display *.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>

https://bugzilla.gnome.org/show_bug.cgi?id=692851

clutter/clutter-backend.c

@@ -1322,7 +1322,7 @@ clutter_backend_get_cogl_context (ClutterBackend *backend)
  * Stability: unstable
  */
 void
-clutter_wayland_set_compositor_display (struct wl_display *display)
+clutter_wayland_set_compositor_display (void *display)
 {
   if (_clutter_context_is_initialized ())
     {