Started moving some X11 window management code to windows/x11drv.

diff --git a/include/acconfig.h b/include/acconfig.h
index 66ece2f..9934a39 100644
--- a/include/acconfig.h
+++ b/include/acconfig.h
@@ -18,6 +18,9 @@
 /* Define if you have the Xxf86dga library (-lXxf86dga).  */
 #undef HAVE_LIBXXF86DGA
 
+/* Define if you have the X Shm extension */
+#undef HAVE_LIBXXSHM
+
 /* Define if you have the Open Sound system.  */
 #undef HAVE_OSS