util: Marked args as unused for compiler in X Error handlers

When an error occurs in X, the Xlib is using a callback mechanism to
execute application code to handle the problem, which means having a
fixed argument list for that application function.

It is then correct to not use all the arguments, so this patch adds the
appropriate stuff to avoid a false report from compiler.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

util/wxcopy.c

@@ -48,6 +48,10 @@ static void print_help(void)
 
 static int errorHandler(Display * dpy, XErrorEvent * err)
 {
+	/* Parameter not used, but tell the compiler that it is ok */
+	(void) dpy;
+	(void) err;
+
 	/* ignore all errors */
 	return 0;
 }