Duplicate function in thread_pthread.h

[Windson Yang]

When I try to understand the code about the thread. I found
the thread_pthread.h file has some duplicate functions. Like
`PyThread_free_lock`, `PyThread_release_lock`,
`PyThread_acquire_lock_timed`. IIUC, C doesn't support function overload.
So why we have functions with the same name and args?
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