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

[Peter Collingbourne via cfe-commits]

pcc wrote:

Also, I just learned that non-standard features are meant to be under `__has_extension` (`EXTENSION` macro) instead of `__has_feature`. See https://github.com/llvm/llvm-project/blob/154354e60e46debb68716cde867cb4e325ce5eb7/clang/include/clang/Basic/Features.def#L20

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