gears: Fail if compiled without cairo-egl
diff --git a/clients/window.h b/clients/window.h
index 42b8b13..6a4ce9f 100644
--- a/clients/window.h
+++ b/clients/window.h
@@ -67,7 +67,7 @@
 EGLConfig
 display_get_argb_egl_config(struct display *d);
 
-void
+int
 display_acquire_window_surface(struct display *display,
 			       struct window *window,
 			       EGLContext ctx);