mconf/nconf: mark empty menus/menuconfigs different from non-empty ones

Submenus are sometimes empty and it would be nice if there is
something that notifies us that we should not expect any content
_before_ we enter a submenu.

A new function menu_is_empty() was introduced and empty menus and
menuconfigs are now marked by "----" as opposed to non-empty ones that
are marked by "--->".

This scheme was suggested by "Yann E. MORIN" <yann.morin.1998@free.fr>.

Signed-off-by: Dirk Gouders <dirk@gouders.net>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
diff --git a/scripts/kconfig/lkc_proto.h b/scripts/kconfig/lkc_proto.h
index ef1a738..ecdb965 100644
--- a/scripts/kconfig/lkc_proto.h
+++ b/scripts/kconfig/lkc_proto.h
@@ -14,6 +14,7 @@
 /* menu.c */
 P(rootmenu,struct menu,);
 
+P(menu_is_empty, bool, (struct menu *menu));
 P(menu_is_visible, bool, (struct menu *menu));
 P(menu_has_prompt, bool, (struct menu *menu));
 P(menu_get_prompt,const char *,(struct menu *menu));