Illumos helgrind: fix for pthread_rwlock_timedrdlock and pthread_rwlock_timedrwlock

Illumos helgrind: fix for pthread_rwlock_timedrdlock and pthread_rwlock_timedrwlock

On Illumos these two functions are implemented by calling
pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock respectively.
Since we intercept both it was appearing as though the lock was being
taken recursively when it wasn't. Fixed it by using a static flag for each
and not callinng the client requests if already in a call to the timed
functions.

I think that musl also does this but, ho-hum, Helgrind has never worked on musl.