Check stdout/stderr of run-pass run portion

[Mark-Simulacrum]

We currently check the compiler's output, but it's sometimes useful to check that the run-pass test itself is outputting the same as before. In particular, @tmandry expressed a desire to test libtest in this fashion.

Taking a look at the code, we probably want to add another header flag (check-run-results) around here in this file; and then when running the generated executable here we should replicate this expected loading code down. If possible, it'd be great to extract some sort of function that would load results and compare them, but I'm not sure how feasible that is in a clean manner.

[Mark-Simulacrum]

I've assigned to @tmandry for now because I believe they might be interested in landing this more quickly than perhaps mentoring will be able to but let us know if you're interested!

[Centril]

This would be great; we could use this to simplify the hacks in testing dbg! for example.

[tmandry]

I would like to get it soon, but I probably won't be getting to this until next week at least :)

[tmandry]

Thanks for providing the mentoring instructions, by the way!

[nathanwhit]

I'm interested in working on this (or rather, I've done some work on this based on the mentoring instructions) if that's okay. Based on what I've done so far, I think I'll be ready to submit a PR within the next day or so.

[nathanwhit]

To test the functionality, I updated the test for the dbg! macro (noted by @Centril) to use the new header flag. Would it be more reasonable to make a separate PR for that once these changes are approved, or could I include it in the same PR? Apologies if this is off-topic.

[Mark-Simulacrum]

Not at all! That seems like a reasonable change to make in the same PR, though it would be good to split it out into a separate commit for easier reviewing. Thanks!