patch 8.0.1570: can't use :popup for a menu in the terminal

Problem:    Can't use :popup for a menu in the terminal. (Wei Zhang)
Solution:   Make :popup work in the terminal.  Also fix that entries were
            included that don't work in the current state.
diff --git a/src/proto/menu.pro b/src/proto/menu.pro
index 4c8e710..63f8d11 100644
--- a/src/proto/menu.pro
+++ b/src/proto/menu.pro
@@ -12,6 +12,7 @@
 int menu_is_child_of_popup(vimmenu_T *menu);
 int menu_is_toolbar(char_u *name);
 int menu_is_separator(char_u *name);
+int get_menu_mode_flag(void);
 void show_popupmenu(void);
 int check_menu_pointer(vimmenu_T *root, vimmenu_T *menu_to_check);
 void gui_create_initial_menus(vimmenu_T *menu);