relax a memory order in once_box

Author: slanterns

library/std/src/sys/sync/once_box.rs

@@ -60,7 +60,7 @@ impl<T> OnceBox<T> {
     #[cold]
     fn initialize(&self, f: impl FnOnce() -> Box<T>) -> &T {
         let new_ptr = Box::into_raw(f());
-        match self.ptr.compare_exchange(null_mut(), new_ptr, AcqRel, Acquire) {
+        match self.ptr.compare_exchange(null_mut(), new_ptr, Release, Acquire) {
             Ok(_) => unsafe { &*new_ptr },
             Err(ptr) => {
                 // Lost the race to another thread.