add where-clause

Author: lcnr

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

@@ -1197,6 +1197,7 @@ where
         // We prefer trivial builtin candidates, i.e. builtin impls without any
         // nested requirements, over all others. This is a fix for #53123 and
         // prevents where-bounds from accidentally extending the lifetime of a
+        // variable.
         let mut trivial_builtin_impls = candidates.iter().filter(|c| {
             matches!(c.source, CandidateSource::BuiltinImpl(BuiltinImplSource::Trivial))
         });