ctest: add tests for size and alignment of structs, unions, and aliases, and signededness of aliases.

[mbyx]

Description

This PR adds tests for verifying size and alignment of struct, union, and typedef types, as well as signededness of alias types (if they are signed).

Sources

Checklist

• Relevant tests in libc-test/semver have been updated
• 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

[mbyx]

Not sure what the CI error is, doesn't seem to be related to the PR.