time.strftime() returns a wrong ISO 8601 week number (%V) on OpenBSD

# Bug report `time.strftime()` and `datetime.strftime()` return a wrong ISO 8601 week number (`%V`) on OpenBSD: ``` >>> date(2008, 12, 29).isocalendar()[:2] (2009, 1) >>> date(2008, 12, 29).strftime('%G-%V') '2009-53' ``` The week number is 53 whenever the ISO 8601 week belongs to other year than the calendar year. `%G` and `%u` are correct. This is a bug in OpenBSD's `wcsftime()`; its `strftime()` returns the correct value for the same `struct tm`. Both contain the same obsolete XPG4-1994 override of the already computed week number, but in `strftime.c` it is wrapped in `#ifdef XPG4_1994_04_09` (never defined), and in `wcsftime.c` the guard is missing. Reported to bugs@openbsd.org. We use `wcsftime()` when `HAVE_WCSFTIME` is defined, so we can avoid the broken function on OpenBSD. `HAVE_WCSFTIME` is only used in `Modules/timemodule.c`, and OpenBSD only supports the C and UTF-8 encodings for `LC_CTYPE`, so decoding the result of `strftime()` with the locale encoding is safe there. This also causes 16 failures in `test_strptime`. <!-- gh-linked-prs --> ### Linked PRs * gh-154461 <!-- /gh-linked-prs -->