cmd/dist: fix install cmd/5g on non-arm system
cmd/dist: fix install cmd/5g on non-arm system

R=golang-dev, r
CC=golang-dev
http://codereview.appspot.com/5689072
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go