Ensure that pre-2000 and post-2050 dates get rejected, and something in
between gets accepted.
This also extends coverage to 100% - before, the post-2050 branch was
not covered.
Both aarch64 and s390x have a bigger wtmp record size (16 bytes more
than x86_64, 400 bytes total).
The byte position of the timestamp is also different on each
architecture. To make things even more interesting, s390x is big endian.
Fixes: https://bugzilla.opensuse.org/show_bug.cgi?id=1181155