add comment and link to test

Author: JohnTitor

tests/ui/traits/next-solver/undeclared-lifetime-no-ice-issue-151461.rs

@@ -1,3 +1,7 @@
+// Regression test for <https://github.com/rust-lang/rust/issues/151461>.
+//
+// The next solver normalizes `TypeOutlives` goals before registering them as region obligations.
+// This should not ICE when we already emitted an error for an undeclared lifetime.
 //@ compile-flags: -Znext-solver=globally
 
 trait X<'a> {

tests/ui/traits/next-solver/undeclared-lifetime-no-ice-issue-151461.stderr

@@ -1,5 +1,5 @@
 error[E0261]: use of undeclared lifetime name `'a`
-  --> $DIR/undeclared-lifetime-no-ice-issue-151461.rs:9:33
+  --> $DIR/undeclared-lifetime-no-ice-issue-151461.rs:13:33
    |
 LL |     for<'b> <Self as X<'b>>::U: 'a,
    |                                 ^^ undeclared lifetime