Update Semaphore::timed_wait with sem_clockwait and converting domain

[Flw5469]

Fix according to #795

1. Use sem_clockwait if available
2. Else use sem_timedwait and convert time parameter's domain from ClockMonotonic into ClockUnix

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[gavv]

I haven't looked at the PR yet (let me know when it's ready), but I've checked how we could detect if sem_clockwait is available.

Seems that POSIX doesn't define any useful macro. The function was introduced in POSIX-2017, but they didn't bump _POSIX_VERSION and it's the same for POSIX-2008 and POSIX-2017.

So seems we should check it in the build system. You can add this to SConstruct before conf.Finish() call:

# feature availability
if conf.CheckFunc('sem_clockwait', header='#include <unistd.h>'):
    conf.env.Append(CPPDEFINES=['ROC_HAVE_SEM_CLOCKWAIT'])

env = conf.Finish()

..and then you can use #ifdef ROC_HAVE_SEM_CLOCKWAIT

[gavv]

Moved to #814