runtime: fix build on openbsd
runtime: fix build on openbsd

R=golang-dev, jsing
CC=golang-dev
https://codereview.appspot.com/7312104

Committer: Joel Sing <55495163370d1a3b8fc0c7106120704aaf8de7f9@google.com>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go