[clang] [Clang] Remove AArch64TargetInfo::setArchFeatures (PR #146107)

[Sander de Smalen via cfe-commits]

sdesmalen-arm wrote:

> Are any of the values set here now dead?

Even if the `HasXXX` variable is not used for setting a preprocessor macro, they're still used by `AArch64TargetInfo::hasFeature`. I hope we can remove this interface in the future in favour of using the FeatureMap approach, which would return the correct predicate on a per-function level (e.g. when using the `target` attribute), but I'm not sure if there are some subtle reasons why this hasn't been done already.

https://github.com/llvm/llvm-project/pull/146107