Which definitely is not what we want here. Use clock_get_time() on a
CALENDAR_CLOCK instead, that gives time since the Unix epoch.

So our osl_getSystemTime() had been completely broken on OS X since
May 19 (d8d55787) and no unit test had
noticed... Fairly coincidentally, an assert() introduced yesterday in
4d220882 caught it.

Change-Id: Iad76a7aadc39159fdc80c99087bb527d6aa49c66