[clang] [compiler-rt] [llvm] [FMV][AArch64] Add feature CSSC and detect on linux platform. (PR #132727)

[Alexandros Lamprineas via llvm-commits]

labrinea wrote:

Hi @jroelofs @DanielKristofKiss. I am not sure how to detect on other platforms. Suggestions for apple and windows welcome.

https://github.com/llvm/llvm-project/pull/132727