[CGData] Rewrite tests to not use subshells
Subshells are not supported by lit's internal shell, which we want to
enable by default for the LLVM test suite. Rewrite the tests in
llvm/test/tools/llvm-cgdata to not use subshells so we can achieve this
without losing any test coverage.
Reviewers: kyulee-com, petrhosek, ilovepi
Reviewed By: ilovepi, petrhosek
Pull Request: https://github.com/llvm/llvm-project/pull/157234
