Improve commit in revision 109542.

Improve commit in revision 109542.

 src/w32fns.c <w32_unicode_gui>: New static variable.
 (globals_of_w32fns): Initialize it according to os_subtype.
 (w32_init_class, w32_msg_pump, w32_wnd_proc): Use it instead of
 testing os_subtype.