[clang] [compiler-rt] [AArch64] Implement __builtin_cpu_supports, compiler-rt tests. (PR #82378)

[via cfe-commits]

DanielKristofKiss wrote:

Backward\forward compatibility force us to support any parameter in `__builtin_cpu_supports `. 
A given codebase and toolchain add support for a new feature and everything works but we can't assume all cases the toolchain is up to date where the project is used so an older version of the compiler needs to accept the new feature string when it doesn't know about it. 
Also target and such a preprocessor checks will not help in this case.

https://github.com/llvm/llvm-project/pull/82378