rerunning on fixpoint change on overflow with non-trivial constraints

[lcnr]

we do this

it's pointless as we do not apply any constraints if a goal encountered overflow.

https://github.com/rust-lang/rust/blob/1f44f0a66fa0892ca680a26e271d22993d53de5c/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs#L401-L417

given that we now always discard overflow, we should probably just clear the query result inside of the query instead of in the caller 😅

[lcnr]

changed in rust-lang/rust#130273