To-be-released NetBSD 7.1.1 reportedly fixes the kernel panic that was
affecting our builders and is being released because of Go's warning.

So, soften our warning.

7.1.1 might work, but I can't get a builder up and running to verify
yet as it appears that Anita either doesn't support it yet, or the
NetBSD CDN doesn't have the files yet.

Change-Id: Ifaafc566879a6afdf1174e545ad10e240da427e8
Reviewed-on: https://go-review.googlesource.com/47970Reviewed-by: Ian Lance Taylor <iant@golang.org>