[libc][semaphore] Add feature for posix semaphore in libc

[Pengxiang-Huang]

We can add posix semaphore feature: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/semaphore.h.html

On Linux, this can be implemented on top of futex-based synchronization.

Implementation for this feature can be split into 4 pr:

• internal semaphore class, unnamed semaphores lifetime: sem_init, sem_destroy, sem_getvalue; [libc][semaphore] Add internal unnamed semaphore implementation #190851

• internal named semaphores lifetime: sem_open, sem_close, sem_unlink

• internal blocking wait/post operations: sem_post, sem_wait, sem_trywait, sem_timedwait, sem_clockwait

• apply sem_t class on internal semaphore

[llvmbot]

@llvm/issue-subscribers-libc

Author: Pengxiang Huang (Pengxiang-Huang)

Details

We can add posix semaphore feature: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/semaphore.h.html

On Linux, this can be implemented on top of futex-based synchronization.

Implementation for this feature can be split into 3 pr:

• unnamed semaphores: sem_t, sem_init, sem_destroy, sem_getvalue

• named semaphores: sem_open, sem_close, sem_unlink

• blocking wait/post operations: sem_post, sem_wait, sem_trywait, sem_timedwait, sem_clockwait