[clang] Revert "[clang][NFC] Refactor flag enum caching (#210632)" (PR #223244)

[Matthias Wippich via cfe-commits]

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

Okay, I'm done with my own analysis of this. What I had in mind requires a bit more change than I anticipated.

Reverting seems like an appropriate action at this point. Thanks.

https://github.com/llvm/llvm-project/pull/223244