macosx: added forgotten method declaration in header file

(cherry picked from commit 58fac8cfd783beffd1840ba688663268513aef83)

modules/gui/macosx/misc.h

@@ -68,6 +68,8 @@
 
 - (void)setCanBecomeKeyWindow: (BOOL)canBecomeKey;
 
+- (void)setCanBecomeMainWindow: (BOOL)canBecomeMain;
+
 /* animate mode is only supported in >=10.4 */
 - (void)orderFront: (id)sender animate: (BOOL)animate;