Relax the `pthread_kill` result assertion in `pkd_stop` to tolerate
`ESRCH`, and guard against only `EINVAL` and `ENOTSUP`.
On macOS what can happen is that the `pthread_kill` returns `ESRCH` due
to the accept thread being already terminated. For that case, the
teardown path should proceed to `pthread_join`.
Testing notes:
- On my macOS setup I consistently encountered `ESRCH` in this
codepath, causing pkd tests to fail unnecessarily. With the
change, I observe the tests passing.
Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit aa206cbfe5)