SPMI: More information on CI failures

[jakobbotsch]

This enhances parts of the SPMI process with more information on failures.

Also fixes a bug I introduced when I added tpdiffs: when asmdiffs fails, it was not marking the entire pipeline as failing.

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Issue Details

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We've seen some SPMI diffs fail due to the JitStdOutFile not existing after running the subprocess. This throws an error with some more information in those case.

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[BruceForstall]

I'll go ahead and approve in case I'm wrong about needing to remove the existing proc.communicate line, or in case you can fix it and merge with the fix long before I wake up so we can make progress investigating this issue.

[jakobbotsch]

@BruceForstall I've updated this PR with some more enhancements, can you please take another look?
The changes are:

• Stop passing -v q to superpmi when creating dasm files, since we now use JitStdOutFile and this was hiding failures
• Make sure we also fail on superpmi sub process failure with more information (previously, we would hide these failures if the JitStdOutFile ended up being created)
• Fix superpmi_diffs.py to properly return a failure error code when asmdiffs fails. This should mark CI as failing in this case so it is more visible. This was a bug introduced by me with the tpdiff support.

[BruceForstall]

LGTM.

When you said "fail on superpmi sub process failure" I thought maybe you'd fixed #56506. Oh well :-)

[jakobbotsch]

When you said "fail on superpmi sub process failure" I thought maybe you'd fixed #56506. Oh well :-)

Afraid not. I think the ideal way to fix that is if we can start using threads instead of processes. Would simplify a lot of other things, too, like if we want to add compression support.