address compilation warnings from gcc

src/windows.c

@@ -133,16 +133,15 @@ const char *mesg;
     return 0;
 }
 
+/*ARGSUSED*/
 void
 genl_preference_update(pref)
 const char *pref;
 {
-	extern struct wc_Opt wc_options[];	/* in options.c */
 	/* window ports are expected to provide
 	   their own preference update routine
 	   for the preference capabilities that
 	   they support.
 	   Just return in this genl one. */
-	return;
 }
 /*windows.c*/