[SystemZ][ZOS] Provide CLOCK_MONOTONIC alternative
We need CLOCK_MONOTONIC equivalent implementation for z/OS within libc++. The default implementation is asserting.
On z/OS the lack of 'clock_gettime()' and 'time_point()' force us to look for alternatives.
The current proposal is to use `gettimeofday()` for CLOCK_MONOTONIC which is also used in CLOCK_REALTIME. This will allow us to skip the assertion with compromised CLOCK_MONOTONIC implementation which will not guarantee to never go back in time because it will use `gettimeofday()` but only when it's set.
Is this a good compromise for platforms which does not support monotonic clock?
Hopefully this will spark the discussion and agreement how to proceed in this situation.
Reviewed By: #libc, ldionne, hubert.reinterpretcast
Differential Revision: https://reviews.llvm.org/D93542
3 files changed