Highlight an error that can only happen in CTFE

Author: oli-obk

src/librustc_middle/mir/interpret/error.rs

@@ -438,7 +438,7 @@ impl fmt::Debug for UndefinedBehaviorInfo {
 /// Error information for when the program did something that might (or might not) be correct
 /// to do according to the Rust spec, but due to limitations in the interpreter, the
 /// operation could not be carried out. These limitations can differ between CTFE and the
-/// Miri engine, e.g., CTFE does not support casting pointers to "real" integers.
+/// Miri engine, e.g., CTFE does not support dereferencing pointers at integral addresses.
 ///
 /// Currently, we also use this as fall-back error kind for errors that have not been
 /// categorized yet.