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

[via cfe-commits]

DanielKristofKiss wrote:

> Hello,
> 
> This patch makes the second line fail to compile
> 
> ```
> #elif ABSL_HAVE_BUILTIN(__builtin_cpu_supports)
>   if (__builtin_cpu_supports("avx2")) {
> ```
> 
> `error: invalid cpu feature string for builtin` when built on arm

expected to fail as __builtin_cpu_supports now supported on Arm too, something like this would be better: 
`#elif ABSL_HAVE_BUILTIN(__builtin_cpu_supports) && (defined(__x86_64__) || defined(__i386__)`



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