Add more from the std

crates/std/src/sys/sync/once/no_threads.rs

@@ -39,6 +39,11 @@ impl Once {
         Once { state: Cell::new(State::Incomplete) }
     }
 
+    #[inline]
+    pub const fn new_complete() -> Once {
+        Once { state: Cell::new(State::Complete) }
+    }
+
     #[inline]
     pub fn is_completed(&self) -> bool {
         self.state.get() == State::Complete