Rollup merge of rust-lang#83440 - fee1-dead:core-cell-intralink, r=jyn514

Use intra-doc link in core::cell

``@rustbot`` label T-doc A-intra-doc-links

r? ``@jyn514``

Author: JohnTitor

library/core/src/cell.rs

@@ -188,7 +188,7 @@
 //! [`Rc<T>`]: ../../std/rc/struct.Rc.html
 //! [`RwLock<T>`]: ../../std/sync/struct.RwLock.html
 //! [`Mutex<T>`]: ../../std/sync/struct.Mutex.html
-//! [`atomic`]: ../../core/sync/atomic/index.html
+//! [`atomic`]: crate::sync::atomic
 
 #![stable(feature = "rust1", since = "1.0.0")]