Auto merge of #2041 - pfmooney:illumos-timers, r=JohnTitor
Auto merge of #2041 - pfmooney:illumos-timers, r=JohnTitor

Add timer interface for illumos and Solaris

This adds the `timer_*` family of functions present in illumos (and Solaris), along with the associated types.  The `libc-test` suite passes on an illumos (OmniOSCE) machine.  While I do not have resources available to test on Solaris, these interfaces have been stable since Oracle forked.

rust-lang/libc,rust-lang/libc,rust-lang/libc