Suppress unused variable warning when compiling without a window system.

src/ChangeLog

@@ -1,3 +1,8 @@
+2013-09-22  Daniel Colascione  <dancol@dancol.org>
+
+	* xfns.c (x_get_monitor_attributes): Suppress unused variable
+	warning when compiling without a window system.
+
 2013-09-22  Daniel Colascione  <dancol@dancol.org>
 
 	* data.c (Qbool_vector_p): New symbol.

src/xfns.c

@@ -3949,6 +3949,8 @@ x_get_monitor_attributes (struct x_display_info *dpyinfo)
   Lisp_Object attributes_list = Qnil;
   Display *dpy = dpyinfo->display;
 
+  (void) dpy; /* Suppress unused variable warning.  */
+
 #ifdef HAVE_XRANDR
   int xrr_event_base, xrr_error_base;
   bool xrr_ok = false;