Rollup merge of #134046 - lqd:new-solver-hangs, r=compiler-errors

Remove ignored tests for hangs w/ new solver

As asked on zulip [here](https://rust-lang.zulipchat.com/#narrow/channel/364551-t-types.2Ftrait-system-refactor/topic/needs_help.3A.20look.20through.20compare-mode.20hangs).

As far as I can tell there are no more UI tests that hang anymore, so this removes the ignore directives for the compare mode.

(As I was using `--compare-mode new-solver` and that failed in an obscure way without any info about what to do, I've also fixed its error handling in `compiletest`: it didn't show the invalid `--compare-mode`, nor the valid values one can pass).

r? lcnr

Author: matthiaskrgr