If a C name must be extern on some platforms, make it extern on all.

If a C name must be extern on some platforms, make it extern on all.

* dispextern.h (set_vertical_scroll_bar, erase_phys_cursor)
(load_color):
* font.h (ftxfont_driver) [HAVE_XFT]:
* keyboard.h (menu_items_inuse, ignore_mouse_drag_p, make_ctrl_char):
* lisp.h (get_frame_param):
* menu.h (tty_menu_show):
* process.h (conv_sockaddr_to_lisp, catch_child_signal):
* termhooks.h (encode_terminal_code):
* xterm.h (x_menu_wait_for_event):
Always declare.
* frame.c (get_frame_param):
* fringe.c (max_used_fringe_bitmap):
* ftxfont.c (ftxfont_driver):
* keyboard.c (ignore_mouse_drag_p, make_ctrl_char):
* menu.c (menu_items_inuse):
* process.c (conv_sockaddr_to_lisp, catch_child_signal):
* term.c (encode_terminal_code, tty_menu_show):
* xdisp.c (set_vertical_scroll_bar, erase_phys_cursor):
* xfaces.c (load_color):
* xmenu.c (x_menu_wait_for_event):
Now always extern.