static SPIN_LOCK: AtomicUsizeAvailable on non-
miri and (Linux or FreeBSD or GNU/Hurd or macOS or NetBSD or OpenBSD or Solaris or illumos) only.static SPIN_LOCK: AtomicUsizemiri and (Linux or FreeBSD or GNU/Hurd or macOS or NetBSD or OpenBSD or Solaris or illumos) only.