Wrapper type for os_unfair_lock

UnfairLock.swift

class UnfairLock: NSLocking {
    private var _lock = os_unfair_lock()

    func lock() {
        os_unfair_lock_lock(&_lock)
    }

    func unlock() {
        os_unfair_lock_unlock(&_lock)
    }

    func `try`() -> Bool {
        return os_unfair_lock_trylock(&_lock)
    }
}