Fix lost wake-up when pthread_rwlock_timedrwlock times out.

Fix lost wake-up when pthread_rwlock_timedrwlock times out.

If we set up a rwlock to prefer writers (and disallow recursive rdlock
acquisitions), then readers will block for writers that are blocked to
acquire the lock (otherwise, readers could constantly enter and exit,
and the writer would never get the lock).  However, the existing
implementation did not wake such readers when the writer timed out.
This patch adds the missing wake-up.
There's no similar case for writers being blocked on readers.