Update Redox's signal constants

[daxtens]

Description

Redox changed its signal ABI last year. The old definitions (unsurprisingly) cause weird crashes. Use the new ones from Redox's relibc.

Sources

https://gitlab.redox-os.org/redox-os/relibc/-/commit/63509e75ce127fdb05c07a464e975687e8ef2977

Checklist

I'm still working out how to run tests inside of redox, so I'm leaving this as a draft until I figure that out.

• Relevant tests in libc-test/semver have been updated (No update required)
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @tgross35 (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[tgross35]

@rustbot author since this is a draft (comment @rustbot review when it's ready for a look)

Were you able to figure the tests out? cargo t does the basics, following or directly running the ci scripts should get everything else.

[daxtens]

I am working on actually getting the libc tests compiled for redox and installed into a redox image - once I do I will update the PR and ask rustbot to change the label, but it might take a while as this is very much a spare-time thing.