sync/atomic: support NetBSD/ARM (ARM11 or above)
sync/atomic: support NetBSD/ARM (ARM11 or above)

R=golang-dev, rsc, dave
CC=golang-dev
https://codereview.appspot.com/7287044
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go