[HAVE_NTGUI] (set_menu_framebar): Declare external.

[HAVE_NTGUI] (set_menu_framebar): Declare external.
[HAVE_NTGUI] (frame_title_buf, frame_title_ptr): Include variables
for Win32 window system.
[HAVE_NTGUI] (store_frame_title, x_consider_frame_title): Include
procedures for Win32 window system.
[HAVE_NTGUI] (x_consider_frame_title): Test for Win32 frame.
[HAVE_NTGUI] (display_text_line): Test for Win32 frame on face change.
[HAVE_NTGUI] (display_menu_bar): Perform no-op for NT window system.

(update_menu_bar, redisplay_window): Test for definition
of FRAME_EXTERNAL_MENU_BAR before using it.

Use FRAME_WINDOW_P of FRAME_EXTERNAL_MENU_BAR before using it.

Use HAVE_WINDOW_SYSTEM instead of testing for specific window systems.