ctest: allow variadics to be tested.

[mbyx]

Description

Removes the check for variadics and adds support for translating variadic types between C and Rust.

While not used currently, might be useful down the line, especially if we ever decide to stop using void pointers for foreign function tests.

Closes #4367

Checklist

• Relevant tests in libc-test/semver have been updated
• Commit messages permalink to headers for added or changed API
• Placeholder or unstable values like *LAST or *MAX have the standard
  doc comment
• Tested locally (cargo test -p libc-test --target mytarget);
  especially relevant for platforms that may not be checked in CI

@rustbot label +stable-nominated

[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.

[tgross35]

Awesome! Thank you

View changes since this review