[gtk+] gtk: x: fix compilation without x11 backend

[Lionel Landwerlin <llandwerlin src gnome org>]

commit 015bf99816969cff366e201169e6c54fd8b3cf3d
Author: Lionel Landwerlin <llandwerlin gmail com>
Date:   Sat Feb 7 20:05:18 2015 +0000

    gtk: x: fix compilation without x11 backend
    
    https://bugzilla.gnome.org/show_bug.cgi?id=744148

 gtk/gtkx-autocleanups.h |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtkx-autocleanups.h b/gtk/gtkx-autocleanups.h
index 3705ff4..bc200a0 100644
--- a/gtk/gtkx-autocleanups.h
+++ b/gtk/gtkx-autocleanups.h
@@ -19,9 +19,13 @@
 #error "Only <gtk/gtkx.h> can be included directly."
 #endif
 
+#ifdef GDK_WINDOWING_X11
+
 #ifndef __GI_SCANNER__
 
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(GtkSocket, g_object_unref)
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(GtkPlug, g_object_unref)
 
 #endif
+
+#endif