xwayland: Introduce a private struct for XWayland interface

libweston-desktop implements this private struct.

Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Jonas Ã…dahl <jadahl@gmail.com>
Acked-by: Giulio Camuffo <giulio.camuffo@kdab.com>

Differential Revision: https://phabricator.freedesktop.org/D1208
diff --git a/libweston/compositor.h b/libweston/compositor.h
index f992263..beda341 100644
--- a/libweston/compositor.h
+++ b/libweston/compositor.h
@@ -778,10 +778,15 @@
 	void (*restore)(struct weston_compositor *compositor);
 };
 
+struct weston_desktop_xwayland;
+struct weston_desktop_xwayland_interface;
+
 struct weston_compositor {
 	struct wl_signal destroy_signal;
 
 	struct wl_display *wl_display;
+	struct weston_desktop_xwayland *xwayland;
+	const struct weston_desktop_xwayland_interface *xwayland_interface;
 	struct weston_shell_interface shell_interface;
 
 	/* surface signals */