vkd3d: Do not allow synchronization primitives to fail.

In practice they never fail. If they fail, it means that there is some underlying platform problem and there is little we can do anyway. Under pthreads function prototypes allow returning failure, but that's only used for "error checking" mutexes, which we don't use.

On the other hand, error handling in vkd3d is rather inconsistent: sometimes the errors are ignored, sometimes logged, sometimes passed to the caller. It's hard to handle failures appropriately if you can't even keep your state consistent, so I think it's better to avoid trying, assume that synchronization primitives do not fail and at least have consistent logging if something goes wrong.