Implement CreateSemaphoreExA/W via CreateSemaphoreA/W

[stephentoub]

Any managed code that touches the ThreadPool is currently crashing when the ThreadPool tries to initialize. This is due to it creating a semaphore via CreateSemaphoreEx in the pal, and those functions not being implemented.

To help make forward progress, this commit just implements those functions simply by delegating to their non-Ex counterparts, ignoring the additional arguments that come with the Ex versions. With this change, ThreadPool.QueueUserWorkItem, Task.Run, etc. are able to successfully schedule work and have it executed.

I've left the "TODO: Implement this!" comments in place, under the assumption that these implementations are shortish-term workarounds.

[janvorli]

Thanks Steve. It looks like the dwFlags are reserved parameter and must be zero and the CreateSemaphoreExW is used only through the following macro:

#define WszCreateSemaphore(_secattr, _count, _maxcount, _name) CreateSemaphoreExW((_secattr), (_count), (_maxcount), (_name), 0, SEMAPHORE_ALL_ACCESS)

So the only value of the dwDesiredAccess is the SEMAPHORE_ALL_ACCESS. That means that your implementation is complete for the current usage. I'd recommend just asserting that the dwDesiredAccess is the SEMAPHORE_ALL_ACCESS.

[stephentoub]

Thanks, Jan. I added the assert and updated the associated comment.

[janvorli]

LGTM