Implementing building two separate binaries for x11 and wayland

Build gnome-shell for x11, and gnome-shell-wayland for wayland
(as well as the associated libgnome-shell and libgnome-shell-wayland).
The first one links to libmutter, the second to libmutter-wayland.

libgnome-shell and libgnome-shell-wayland are now compiled from
libgnome-shell-base (with all sources that are independent of mutter),
libgnome-shell-menu (with the copy-pasted gtk sources), plus the
sources that use mutter API

https://bugzilla.gnome.org/show_bug.cgi?id=705497

src/main.c

@@ -388,6 +388,7 @@ main (int argc, char **argv)
 
   ctx = meta_get_option_context ();
   g_option_context_add_main_entries (ctx, gnome_shell_options, GETTEXT_PACKAGE);
+  g_option_context_add_group (ctx, g_irepository_get_option_group ());
   if (!g_option_context_parse (ctx, &argc, &argv, &error))
     {
       g_printerr ("%s: %s\n", argv[0], error->message);