nptl: Fix tst-cancel30 on kernels without ppoll_time64 support

Fall back to ppoll if ppoll_time64 fails with ENOSYS.
Fixes commit 370da8a1 ("nptl: Fix
tst-cancel30 on sparc64").

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
(cherry picked from commit f4724843)