syscall: fix mingw build
syscall: fix mingw build

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/988042

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go