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

[Avi Kivity via cfe-commits]

avikivity wrote:

> > I'm afraid I don't know this code at all.
> 
> No worries, if you need me to take over just let me know - I might be able to cram it into next week's schedule.

I'm not proposing to do anything besides this revert.

> 
> > IMO not breaking existing code takes precedence. Maybe I'm biased because it's my code that's getting broken
> 
> Sure but if there's ways to avoid undoing work, we should explore them - especially given that this refactor was in preparation for a larger, more interesting patch. Reverting isn't the only way to deal with unintentional breaks :P

That's up to llvm community standards, but I think it's much better to quickly revert to avoid harm to others, and then redo the original patch more carefully. Undoing the revert is a click away, it's not like anything is really lost.

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