Adjust language to also cover named constants

Especially since it seems that there is no test in rust-lang/rust that
covers the unamed constant case (even though the implementation covers
it). rust-lang/rust#93838 (comment)

Author: cameraMeasurementTech

src/items/constant-items.md

@@ -89,10 +89,15 @@ m!(const _: () = (););
 // const _: () = ();
 ```
 
-Unnamed constants are always [evaluated][const_eval] at compile-time to surface
+## Evaluation
+
+[Free][free] constants are always [evaluated][const_eval] at compile-time to surface
 panics. This happens even within an unused function:
 
 ```rust,compile_fail
+// Compile-time panic
+const PANIC: () = std::unimplemented!();
+
 fn unused_generic_function<T>() {
     // A failing compile-time assertion
     const _: () = assert!(usize::BITS == 0);