Add clock_nanosleep()

[Gedare Bloom]

The clock_nanosleep function is provided to enable specifying the clock source (CLOCK_REALTIME or CLOCK_MONOTONIC) and to control whether or not to use an absolute or relative reference point via TIMER_ABSTIME flag.

See also: ​http://pubs.opengroup.org/onlinepubs/009695399/functions/clock_nanosleep.html

[Gedare Bloom <gedare@…>]

In e0f17fcf6f06d3383cd389d809ee4e3d6e0fb14d/rtems:

posix: fix clock_nanosleep and nanosleep clock use

Sleeping with CLOCK_REALTIME should use the WATCHDOG_ABSOLUTE
clock discipline for the threadq so that the timeout interval
may change in case the clock source changes. Similarly,
CLOCK_MONOTONIC uses the WATCHDOG_RELATIVE threadq that will
only wakeup the thread after the requested count of ticks elapse.

updates #2732

[Gedare Bloom <gedare@…>]

In 39d97ab78cfcc37eb8b1e7d9f9717f51b249155b/rtems:

cpukit: refactor nanosleep and use 64-bit timeout for threadq

• Fixes a bug with elapsed time calculations misusing absolute time arguments in nanosleep_helper by passing the requested relative interval.
• Fixes a bug with truncation of absolute timeouts by passing the full 64-bit value to Thread_queue_Enqueue.
• Share yield logic between nanosleep and clock_nanosleep.

updates #2732

[Gedare Bloom <gedare@…>]

In 842005e432136953d670e39cedc2d665ea949e7b/rtems:

posix: nanosleep: optimize away a time conversion

updates #2732

[Gedare Bloom <gedare@…>]

In 709594f0fb29d4f860b99cda264ea3e74c635a72/rtems:

posix: nanosleep: adjust elapsed time calculation

Use clock_gettime before and after sleep to calculate
the time spent asleep, and the amount of time remaining.

updates #2732

[Sebastian Huber]

Milestone renamed