patch 8.2.0320: no Haiku support

Problem:    No Haiku support.
Solution:   Add support for Haiku. (Emir Sari, closes #5605)

src/structs.h

@@ -3643,6 +3643,13 @@ struct VimMenu
     HMENU	submenu_id;	    // If this is submenu, add children here
     HWND	tearoff_handle;	    // hWnd of tearoff if created
 #endif
+#if FEAT_GUI_HAIKU
+    BMenuItem  *id;		    // Id of menu item
+    BMenu  *submenu_id;		    // If this is submenu, add children here
+# ifdef FEAT_TOOLBAR
+    BPictureButton *button;
+# endif
+#endif
 #ifdef FEAT_GUI_MAC
 //  MenuHandle	id;
 //  short	index;		    // the item index within the father menu