strerror, strsignal, and their variants should return unique strings for
each known (and, depending on the function, unknown) error/signal. Add
tests to verify this for strerror, strerror_r (GNU and XSI compliant
variants), and strerror_l (for the C locale), strerrordesc_np,
strsignal, sigabbrev_np, and sigdescr_np.
Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>