LibJS: Implement Atomics.compareExchange

Author: https://github.com/trflynn89
Commit: 33eb830929
Pull-request: https://github.com/SerenityOS/serenity/pull/8752
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/Runtime/AtomicsObject.h

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(add);
     JS_DECLARE_NATIVE_FUNCTION(and_);
+    JS_DECLARE_NATIVE_FUNCTION(compare_exchange);
     JS_DECLARE_NATIVE_FUNCTION(exchange);
     JS_DECLARE_NATIVE_FUNCTION(load);
     JS_DECLARE_NATIVE_FUNCTION(or_);