[clang] Add fine-grained `__has_feature()` cutout (PR #170822)

[via cfe-commits]

j39m wrote:

I've been waiting on the `build and test {linux,windows}` steps for a few days now. Is there something I need to do to make them resolve?

I will still need a hint on what build target to use to repro the failure in my tree.

https://github.com/llvm/llvm-project/pull/170822