unix: add arm64/linux support

This incorporates generation script changes from
http://golang.org/cl/7143.

Files generated on Ubuntu Trusty.

Change-Id: I28cfa0993573e1b280c549a67f453c0fb01dee2f
Reviewed-on: https://go-review.googlesource.com/10038
Reviewed-by: Rob Pike <r@golang.org>
8 files changed