WINGs: Marked args as unused for compiler in Notification callback code

The mechanism of Notifications in the WINGs toolkit is relying on
callbacks to dispatch notifications, which means having a fixed argument
list for the handling 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>

WINGs/wslider.c

@@ -49,6 +49,9 @@ static void makeKnobPixmap(Slider * sPtr);
 
 static void realizeObserver(void *self, WMNotification * not)
 {
+	/* Parameter not used, but tell the compiler that it is ok */
+	(void) not;
+
 	makeKnobPixmap(self);
 }