Should be in system headers, but not specified by any standard.
Not currently used anywhere yet.
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
This adds monotime() to retrieve monotonic clock time, as well as
monotime_since() and monotime_until() for relative monotonic time.
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>