Rollup merge of rust-lang#33563 - Amanieu:oncestate, r=alexcrichton

Export OnceState from libstd

This type is used in the signature of `call_once_force` but isn't exported from libstd.

r? @alexcrichton

src/libstd/sync/mod.rs

@@ -31,7 +31,7 @@ pub use self::mutex::MUTEX_INIT;
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::mutex::{Mutex, MutexGuard, StaticMutex};
 #[stable(feature = "rust1", since = "1.0.0")]
-pub use self::once::{Once, ONCE_INIT};
+pub use self::once::{Once, OnceState, ONCE_INIT};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use sys_common::poison::{PoisonError, TryLockError, TryLockResult, LockResult};
 #[stable(feature = "rust1", since = "1.0.0")]