cmd/go: fix build

This was missed in c3b45d0dc5c0

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/12379043
cmd/dist: fix windows build.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/12351045

Committer: Brad Fitzpatrick <bradfitz@golang.org>