posix: implement clock_nanosleep()

[ycsin]

There are currently 20 missing POSIX functions with trivial implementations, clock_nanosleep() is one of them.

clock_nanosleep - high resolution sleep with specifiable clock

If the flag TIMER_ABSTIME is not set in the flags argument, the clock_nanosleep() function shall cause the current thread to be suspended from execution until either the time interval specified by the rqtp argument has elapsed, or a signal is delivered to the calling thread and its action is to invoke a signal-catching function, or the process is terminated. The clock used to measure the time shall be the clock specified by clock_id.

If the flag TIMER_ABSTIME is set in the flags argument, the clock_nanosleep() function shall cause the current thread to be suspended from execution until either the time value of the clock specified by clock_id reaches the absolute time specified by the rqtp argument, or a signal is delivered to the calling thread and its action is to invoke a signal-catching function, or the process is terminated. If, at the time of the call, the time value specified by rqtp is less than or equal to the time value of the specified clock, then clock_nanosleep() shall return immediately and the calling process shall not be suspended.

The suspension time caused by this function may be longer than requested because the argument value is rounded up to an integer multiple of the sleep resolution, or because of the scheduling of other activity by the system. But, except for the case of being interrupted by a signal, the suspension time for the relative clock_nanosleep() function (that is, with the TIMER_ABSTIME flag not set) shall not be less than the time interval specified by rqtp, as measured by the corresponding clock. The suspension for the absolute clock_nanosleep() function (that is, with the TIMER_ABSTIME flag set) shall be in effect at least until the value of the corresponding clock reaches the absolute time specified by rqtp, except for the case of being interrupted by a signal.

The use of the clock_nanosleep() function shall have no effect on the action or blockage of any signal.

The clock_nanosleep() function shall fail if the clock_id argument refers to the CPU-time clock of the calling thread. It is unspecified whether clock_id values of other CPU-time clocks are allowed.

See https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock_nanosleep.html

See RFC #51211 for more info.