[clang] [OpenACC] Implement firstprivate lowering except init. (PR #153847)

[Andy Kaylor via cfe-commits]

https://github.com/andykaylor approved this pull request.

This looks good to me. My only question is probably unrelated to this PR, just something that occurred to me as I was looking at the test cases.

https://github.com/llvm/llvm-project/pull/153847