BMenuBar & Deskbar: Make the hack to call ShowMenuBar a lot less ugly.

The previous hack, which as the comment (and __MWERKS__) implies
dates all the way back to the Be era, finally broke: int32 is "int"
on non-x86, not "long", and so this generated an undefined symbol
error on ARM.

The best solution seems to be to make StartMenuBar merely protected,
and then make a subclass where it is fully public to call it.
This is a lot less fragile (and much less ugly.)

Change-Id: I0519d0d9eeb1cc4523d0c6dd4fdfe8688ed1092c
Reviewed-on: https://review.haiku-os.org/c/1516
Reviewed-by: Adrien Destugues <[email protected]>

headers/os/interface/MenuBar.h

@@ -79,6 +79,11 @@ public:
 
 	virtual status_t			Perform(perform_code code, void* data);
 
+protected:
+			void				StartMenuBar(int32 menuIndex,
+									bool sticky = true, bool showMenu = false,
+									BRect* special_rect = NULL);
+
 private:
 	friend class BWindow;
 	friend class BMenuField;
@@ -91,12 +96,6 @@ private:
 
 			BMenuBar			&operator=(const BMenuBar &);
 
-	// TODO: Tracker uses this function so we can't change
-	// its signature without breaking it
-			void				StartMenuBar(int32 menuIndex,
-									bool sticky = true, bool showMenu = false,
-									BRect* special_rect = NULL);
-
 	static	int32				_TrackTask(void *arg);
 			BMenuItem*			_Track(int32 *action, int32 startIndex = -1,
 									bool showMenu = false);