Swap the encoding used in std::sync::Once

Let the fast path (COMPLETE) to use the constant 0.
This may only reduces code sizes by 1 byte on x86/64 but it can
reduce an instruction on RISC ISAs.

Author: nbdd0121

library/std/src/sync/once.rs

@@ -161,10 +161,10 @@ pub const ONCE_INIT: Once = Once::new();
 
 // Four states that a Once can be in, encoded into the lower bits of
 // `state_and_queue` in the Once structure.
-const INCOMPLETE: usize = 0x0;
+const COMPLETE: usize = 0x0;
 const POISONED: usize = 0x1;
 const RUNNING: usize = 0x2;
-const COMPLETE: usize = 0x3;
+const INCOMPLETE: usize = 0x3;
 
 // Mask to learn about the state. All other bits are the queue of waiters if
 // this is in the RUNNING state.