Check expected stdouts/stderrs in expect_broken tests

Currently it's not possible to check stdouts and stderrs of expect_broken tests, so if a test that fails with e.g. segfault starts failing with e.g. an error call unintentionally after a commit we don't realize it.

This happened as I was working on !1381 (closed). My bug fix turned the segfault into an expected failure with undefined, but the test suite happily accepted the test.

I think we should check stdout/stderrs of expect_broken tests as much as possible.