add semaphore using futex_waitv(2) supporting notify_specific

The SpuriousFutex2Semaphore is able to notify a specific worker
by using two futexes two wait on.

One working like a normal semaphore used for global non specific
notifications via notify() and notify_many().

And a second one per worker which is based on a SleeperState.
To notify a specific worker we change its SleeperState to Notified
and call FUTEX_WAKE if needed.