rustc_data_structures: sync and atomic consistency

Co-authored-by: @lukas-code

Author: notriddle

compiler/rustc_data_structures/src/sync.rs

@@ -139,14 +139,14 @@ cfg_if! {
 
         impl Atomic<bool> {
             pub fn fetch_or(&self, val: bool, _: Ordering) -> bool {
-                let result = self.0.get() | val;
-                self.0.set(val);
-                result
+                let old = self.0.get();
+                self.0.set(val | old);
+                old
             }
             pub fn fetch_and(&self, val: bool, _: Ordering) -> bool {
-                let result = self.0.get() & val;
-                self.0.set(val);
-                result
+                let old = self.0.get();
+                self.0.set(val & old);
+                old
             }
         }