Link to tracking issue in HIR const-check error

Author: ecstatic-morse

src/librustc_error_codes/error_codes/E0744.md

@@ -15,3 +15,10 @@ const _: i32 = {
     x
 };
 ```
+
+This will be allowed at some point in the future, but the implementation is not
+yet complete. See the tracking issue for [conditionals] or [loops] in a const
+context for the current status.
+
+[conditionals]: https://github.com/rust-lang/rust/issues/49146
+[loops]: https://github.com/rust-lang/rust/issues/52000