[libcxx-commits] [libcxx] [libc++][test-suite][NFC] Refactor `unused_variables` tests (PR #223234)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 requested changes to this pull request.

I've put this there, since I don't think it's worth having this in multiple files.

https://github.com/llvm/llvm-project/pull/223234