all: enable NetBSD 7.0 builders

Fixes golang/go#8643

Change-Id: Id6a99d0bf4f032c5f5a2e5c282103cc98a515c7b
Reviewed-on: https://go-review.googlesource.com/37469
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
4 files changed