[clang] [llvm] [AArch64][FMV] Add missing feature dependencies and detect at runtime. (PR #119231)

[Alexandros Lamprineas via llvm-commits]

labrinea wrote:

@sdesmalen-arm the dependencies were agreed internally with @paulwalker-arm. Let us know if you have any reservations.

https://github.com/llvm/llvm-project/pull/119231