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.