[clang] [llvm] [AArch64] Decouple feature dependency expansion. (PR #94279)

[Tomas Matheson via llvm-commits]

https://github.com/tmatheson-arm approved this pull request.

LGTM. The main change to point out is that the target attribute will no longer accept internal feature names. I don't think it should ever have done so, but we should get input from others. @davemgreen? There are references to existing code in [D137617](https://reviews.llvm.org/D137617) but no details. If this has been used for e.g. intrinsics definitions, I am surprised there are not more test failures.

https://github.com/llvm/llvm-project/pull/94279