time: Also check for EPERM while trying to clock_settime

Container management default seccomp filter [1] only accepts
clock_settime if process has also CAP_SYS_TIME.  So also handle
EPERM as well.

Also adapt the test to libsupport and add a proper Copyright header.

Checked on aarch64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>