tst-cancel4: deal with ENOSYS errors

The Hurd port doesn't have support for sigwaitinfo, sigtimedwait, and msgget
yet, so let us ignore the test for these when they return ENOSYS.

* nptl/tst-cancel4.c (tf_sigwaitinfo): Fallback on sigwait when
sigwaitinfo returns ENOSYS.
(tf_sigtimedwait): Likewise with sigtimedwait.
(tf_msgrcv, tf_msgsnd): Fallback on tf_usleep when msgget returns ENOSYS.