MFC r275727:
For architectures where time_t is wide enough, in particular, 64bit
platforms, avoid overflow after year 2038 in clock_ct_to_ts().

PR:	195868
MFC r275833:
The iret instruction may generate #np and #ss fault, besides #gp.
When returning to usermode, the handler for that exceptions is also
executed with wrong gs base.  Handle all three possible faults in the
same way, checking for iret fault, and performing full iret.