[lit] Move pipefail test into lit tests

These removes another test that otherwise needs a shell. This does
remove test coverage for pipefail in the external shell, but the
external shell should be disabled by default pretty soon. This also adds
test coverage for the internal shell which did not exist before.

Reviewers: jh7370, ilovepi, petrhosek

Reviewed By: ilovepi, petrhosek

Pull Request: https://github.com/llvm/llvm-project/pull/157223