missing tests cases for clock_nanosleep?

[Joel Sherrill]

Hi

I was looking for test cases for clock_nanosleep(CLOCK_MONOTONIC,...)
and I don't think we have any.

I think psxclockrealtime01 could be repurposed and conditionally
compiled to use either timer.except for the timeout finite case since
you can't set CLOCK_MONOTONIC.

Thoughts?

Thanks.

--joel