Integrate stdarch tests for aarch64

[CathalMullan]

Had a go at wiring up stdarch. Runs the core_arch and intrinsic-test test suites.

Looked into x86 as well. It had more hard errors to resolve up front, so opted to stick with aarch64 for now.

The skip mechanism for these may be a little cumbersome to maintain.
Maybe making the tests opt-in rather than opt-out would be the better approach?

[bjorn3]

Maybe making the tests opt-in rather than opt-out would be the better approach?

Yeah, I think that would work better. Aside from currently being a shorter list, it also avoids mistakenly thinking a new failing test got added that can be disabled just fine rather than an existing test now failing.

[CathalMullan]

Now uses rust-src for the stdarch tests.

Switching from opt-out to opt-in will require some upstream work in stdarch. It only supports STDARCH_TEST_SKIP_FUNCTION / --skip, no mechanism to only run a subset of tests.

The opt-in lists would likely be longer than the existing skip lists fwiw.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[CathalMullan]

Rebased and dropped the lockfile generation.

Refreshed the skip lists as well.
Hit a clang specific failure, so added per $CC skipping too.

The patch approach also needed to be tweaked, now filtering out SVE/SVE2 generated tests manually, due to rust-lang/stdarch#2160.

[bjorn3]

Thanks a lot for implementing this!