[clang] [Clang][Sema] Fix type of enumerators in incomplete enumerations (PR #84068)

[Aaron Ballman via cfe-commits]

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

Aside from some formatting issues, this LGTM. Once you push up a fix for the formatting, I'll land. Thank you!

https://github.com/llvm/llvm-project/pull/84068