This change syncs the lib/libc/c063 NetBSD tests with FreeBSD. This does
two things:
- Addresses bogus tautologically true assertions flagged by clang and gcc
with ATF 0.22+ [1].
- Brings in some new test coverage.
Obtained from: NetBSD (date tag: `20260818UTC`)
MFC after: 2 weeks
1. https://github.com/freebsd/atf/pull/72