Calling __wt_semaphore_wait could fail with EINTR, if the wait is interrupted, such as due to receiving a signal. We need to decide what is the correct way to handle it, and especially whether we should handle it inside __wt_semaphore_wait or in the caller.

Note that the fix has to work for all three supported platforms, and we need to audit the code to ensure that an interrupted wait results in the same error code across all platforms.