[clang] [Clang][Basic] Enable `__has_feature(cfi)` (PR #151348)

[via cfe-commits]

moorabbit wrote:

> If we have `__has_feature(cfi)` mean CFI || KCFI that is sort of going in the opposite direction

Yes.

IMHO, it's a good idea to have a dedicated `__has_feature` for "regular" `CFI`, similar to what we have for `KCFI`.
Merging "regular" `CFI` and `KCFI` support under a single `__has_feature(cfi)` can be awkward, since it doesn’t definitively indicate support for regular `CFI`.

https://github.com/llvm/llvm-project/pull/151348