explicit link to core::os::darwin::objc from std::os::darwin::objc

Author: jbatez

library/std/src/os/darwin/objc.rs

@@ -1,11 +1,13 @@
 //! Defines types and macros for Objective-C interoperability.
 //!
 //! This module re-exports all the items in [`core::os::darwin::objc`].
+//!
+//! [`core::os::darwin::objc`]: ../../../../core/os/darwin/objc/index.html "mod core::os::darwin::objc"
 
 #![unstable(feature = "darwin_objc", issue = "145496")]
 
-// We can't document this automatically since we generate documentation for this module
-// on every platform but `core::os::darwin` isn't available on every platform.
-// We just mention it in the module documentation above instead.
+// We can't generate an intra-doc link for this automatically since `core::os::darwin` isn't
+// compiled into `core` on every platform even though it's documented on every platform.
+// We just link to it directly in the module documentation above instead.
 #[cfg(not(doc))]
 pub use core::os::darwin::objc::*;