Make Rc<T>::deref and Arc<T>::deref zero-cost

Author: EFanZh

library/alloc/src/lib.rs

@@ -212,6 +212,8 @@ mod testing;
 #[macro_use]
 mod macros;
 
+#[cfg(not(no_rc))]
+mod raw_rc;
 mod raw_vec;
 
 // Heaps provided for low-level allocation strategies