Complete in the sense that all POSIX *locale(3) and *_l(3) functions
are included, but in OpenBSD, we of course only really care about
LC_CTYPE and we only support ASCII and UTF-8.

With important help from kettenis@, guenther@, and jca@.
Repeated testing in ports bulk builds by naddy@.
Additional testing by jca@, sebastia@, dcoppa@, and others.
OK kettenis@ dcoppa@, and guenther@ on an earlier version.
Riding guenther@'s libc/librthread major bump.