OK, I've filed the tracking issue for this evaluation:
There are several here that need some bikeshedding still, or where the details are not clear to me:
This also uncovered one new guidelines issue:
What's the bug number for cargo backing out make jobserver support? I implemented that myself one time, maybe I can help.
This sounds like a configure script.
@zackw https://github.com/rust-lang/rust/issues/42635 and the issues linked from there are about cargo's jobserver support.