This wasn't actually generated on freebsd/arm64 yet. It's mostly a copy
of the amd64 files for now.

Updates golang/go#24715

Change-Id: Iee8c12c29f1d74780948553047bc693668dde0b3
Reviewed-on: https://go-review.googlesource.com/c/156499
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>