Description:
------------
As with alot of the PHP extensions some are not thread-safe by nature however posix_strerror could easily be thread-safe by making a small change to the way it operates and as such is fully capable of becoming thread-safe. It is my impression that this use is not thread-safe (I could be wrong).

The problem is that posix_strerror makes a call to strerror() which returns a pointer to the string which may *not* be modified as it is reused and overwritten by the next call to strerror. Instead posix_strerror should call strerror_r which accepts a buffer and buffer length and writes the data there instead.

Granted that PHP seems to be making a copy of the output for its own use there is a possibility of a race condition occurring with other threads. This is just a small potential improvement that shouldnt take much time to implement and would be a a step forward for thread-safety. 

There may be other cases of thread-safety issues in the posix extension but those can be tackled one at a time. This is just a very limited and specific report for one use case. If someone wants to scan the entire extension for said issues more power to them but I am just requesting this particular case be resolved.

Test script:
---------------
<?php
 echo posix_strerror(110);
?>

Expected result:
----------------
No corruption should ever be possible to occur.

Actual result:
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Corruption could possibly occur in a build utilizing multiple threads.