wmaker: Marked args as unused for compiler in XExposeEvent callback code

The custom drawing code for windows is handled using callback functions,
which means having a fixed argument list for that 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>

src/framewin.c

@@ -1378,6 +1378,9 @@ static void handleButtonExpose(WObjDescriptor * desc, XEvent * event)
 	WFrameWindow *fwin = (WFrameWindow *) desc->parent;
 	WCoreWindow *button = (WCoreWindow *) desc->self;
 
+	/* Parameter not used, but tell the compiler that it is ok */
+	(void) event;
+
 #ifdef XKB_BUTTON_HINT
 	if (button == fwin->language_button) {
 		if (wPreferences.modelock)