[Bug 45524] Add a futex-based implementation of condition variables

https://bugs.winehq.org/show_bug.cgi?id=45524

--- Comment #2 from Zebediah Figura  ---
(In reply to Dmitry Timoshkov from comment #1)
> Wouldn't it be more natural to move the futexes support to the underlying
> ntdll implementations of NtWaitForKeyedEvent, etc?

I'm not sure that would work; I had assumed that keyed events didn't have to
use pointers to valid memory as a key. Is this not the case?