Windows NT synchronization primitives for Linux

... with what they have to do if you only have POSIX threads: https://github.com/rust-lang/rust/blob/master/library/std...

Between "It's very stupid but POSIX technically allows this, so we need to cope" on one hand, and people just straight up not complying with POSIX anyway on the other I'd have thrown all of my toys out of the pram before writing the latter monster.

† Technically unlike the C mutex, a Rust Mutex<T> is a wrapper for a type T, the code I've linked isn't about that part, just the part with the actual mechanics of a mutex which are platform specific.