Change loadlocale to fill a __locale_t given as parameter

Don't use global variables.  This allows to call loadlocale from
the yet to be created newlocale().

Rename _thr_locale_t to __locale_t (these locales are not restricted
to threads so the name is misleading).

Along these lines, fix _set_ctype to take a __locale_t as parameter.

Signed-off by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/nlsfuncs.cc

@@ -1070,7 +1070,7 @@ __set_lc_messages_from_win (const char *name,
    LC_COLLATE locale information.  This is subsequently accessed by the
    below functions strcoll, strxfrm, wcscoll, wcsxfrm. */
 extern "C" int
-__collate_load_locale (struct _thr_locale_t *locale, const char *name,
+__collate_load_locale (struct __locale_t *locale, const char *name,
 		       void *f_mbtowc, const char *charset)
 {
   const struct lc_collate_T *ccop;