New module 'setlocale'.

New module 'setlocale'.

* lib/locale.in.h (setlocale): New declaration.
* lib/setlocale.c: New file, based on
gettext/gettext-runtime/intl/setlocale.c.
* m4/setlocale.m4: New file.
* m4/locale_h.m4 (gl_LOCALE_H): Test whether setlocale is declared.
(gl_LOCALE_H_DEFAULTS): Initialize GNULIB_SETLOCALE, REPLACE_SETLOCALE.
* modules/locale (Makefile.am): Substitute GNULIB_SETLOCALE,
REPLACE_SETLOCALE.
* modules/setlocale: New file.
* tests/test-locale-c++.cc: Test the declaration of setlocale.
* doc/posix-functions/setlocale.texi: Mention the new module.