Add stubs for missing GDK windowing functions to Quartz backend

This seems to more or less fix the build.  On Tiger there are still issues
with libresolv missing on the link line, I will figure out what's up with
that soonish.

gdk/quartz/gdkwindow-quartz.c

@@ -2876,6 +2876,27 @@ _gdk_windowing_window_set_composited (GdkWindow *window, gboolean composited)
 {
 }
 
+GdkRegion *
+_gdk_windowing_get_shape_for_mask (GdkBitmap *mask)
+{
+  /* FIXME: implement */
+  return NULL;
+}
+
+GdkRegion *
+_gdk_windowing_window_get_shape (GdkWindow *window)
+{
+  /* FIXME: implement */
+  return NULL;
+}
+
+GdkRegion *
+_gdk_windowing_window_get_input_shape (GdkWindow *window)
+{
+  /* FIXME: implement */
+  return NULL;
+}
+
 static void
 gdk_window_impl_iface_init (GdkWindowImplIface *iface)
 {