Code review comment for lp:~vanvugt/mir/posix-timestamp-or-equal

This looks fine for CLOCK_MONOTONIC.

This is incorrect for CLOCK_REALTIME, or rather, worse, this is misleading for CLOCK_REALTIME. Given CLOCK_REALTIME values a, b:

a < b does not imply that a was before b.
a > b does not imply that a was after b.
a == b does not imply that they refer to the same time.

We should remove these operations for CLOCK_REALTIME; we can't correctly implement them (without a large amount of extra work, and external dependencies)