GitLab

It's more common to specify GOOS/GOARCH values in that order,
rather than the inverse. Fix the order.

Updates #18892.

Change-Id: I8551508599e019f6617dc007397b562c9926418d
Reviewed-on: https://go-review.googlesource.com/120057

Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>