pthread_setspecific returns an errno value, unlike the Sce function it wraps,
and neither POSIX export had a test. Check the FreeBSD 11.4 results of
_pthread_setspecific and _pthread_getspecific (lib/libthr/thread/thr_spec.c
lines 165-194 and 196-222): a key outside the valid range or a deleted key
makes setspecific return EINVAL (22), getspecific returns NULL for such a key
and for a key never set, a stored value is read back, NULL can be stored, a
new key with a reused number starts empty, and another thread has its own
value.
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
