[compiler-rt] [compiler-rt][AArch64] Rewrite SME routines to all use __aarch64_cpu_features. (PR #119414)

[Jon Roelofs via llvm-commits]

jroelofs wrote:

> > On some platforms that happens automatically via an `__attribute__((constructor))` function, but Darwin and Fuchsia don't, and instead rely on an FMV resolver triggering it.
> 
> Is there a technical reason for that or is this just an implementation choice?

All the existing uses of it on Darwin platforms are lazy, and thus you don't pay for what you don't use. And in general, we try really hard to avoid global ctors/dtors as they tend to dirty pages, increase launch times, etc.

https://github.com/llvm/llvm-project/pull/119414