tests: Fix internationalization problems on native Windows. * doc/posix-functions/setlocale.texi: Clarify the deficiency of setlocale() on native Windows. * modules/c-nstrftime-tests (Depends-on): Add setlocale. * modules/dfa-tests (Depends-on): Likewise. * modules/hard-locale-tests (Depends-on): Likewise. * modules/localcharset-tests (Depends-on): Likewise. * modules/nstrftime-tests (Depends-on): Likewise.