localename: Fix test failure on OpenBSD >= 6.2.
* m4/intl-thread-locale.m4 (gt_INTL_THREAD_LOCALE_NAME): Test for fake
locale system. Define HAVE_FAKE_LOCALES in this case.
* lib/localename.c (HAVE_GOOD_USELOCALE): New macro. Use it instead of
HAVE_USELOCALE.
* tests/test-localename.c (HAVE_GOOD_USELOCALE): New macro. Use it
instead of HAVE_NEWLOCALE && HAVE_USELOCALE.
* doc/posix-functions/uselocale.texi: Mention OpenBSD problem. Update
platforms list.
* doc/posix-functions/newlocale.texi: Likewise.
* doc/posix-functions/duplocale.texi: Update platforms list.
* doc/posix-functions/freelocale.texi: Likewise.