pthread: avoid heap alloc in pthread_cond_timedwait if possible (IDFGH-7409)

[MacDue]

This creates the wait sem with xSemaphoreCreateCountingStatic if possible taking around 80 bytes off the stack.
This semaphore is only used for the life of this function, which can be quite heavily called, so this avoids any possible heap/performance issues.

[Alvin1Zhang]

Thanks for your contribution.

[igrr]

This looks like a useful improvement, thank you! Have left one minor comment.

By the way, have you done any benchmarks to see how much this change improves performance?

[MacDue]

I don't think this changes the runtime performance really (since you normally will be waiting at least a few milliseconds in the cond_timedwait).

My main thought with this change was to avoid the possibility of heap fragmentation when waiting for longer timeouts,
though I've not got anything quantifiable for that (it was just something I thought about when looking over the code due to an unrelated issue).

[0xjakob]

sha=c104662192c35ddc01050310ec96705894a75889

[CLAassistant]

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[0xjakob]

@MacDue Your code is available on master already. Because it is merged already, we are closing this PR.