[cpufeatures] aarch64 CPU feature runtime detection do exist on Windows

[be5invis]

There is a user-mode API called IsProcessorFeaturePresent could do this.

https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-isprocessorfeaturepresent

[tarcieri]

I am unfortunately not a Windows user, though that's not to say we don't care about Windows support.

It would be good if someone who regularly develops on Windows can add such support by opening a PR.