help needed with CPU feature detection for aarch64

[Thomas Klausner <wiz%netbsd.org@localhost>]

Hi!

I've reported a problem with the aws-lc{,-sys} crate upstream, and one
of the developers replied that he was working on supporting NetBSD but
had trouble with CPU detection on the aarch64 port.

His C code is here:

https://github.com/aws/aws-lc/pull/2754/files#diff-7ad76e10d4f666572a40a971245531af6078a85543e0ca941b6a01a8e9657c5c

His questions seems to be mostly about how to interpret the
machdep.id_aa64isar0 sysctl result.

He'd be happy about advice here:

https://github.com/aws/aws-lc-rs/issues/932

If you know something about this area, please take a look.

Thank you!
 Thomas