Pases toolstash -cmp.

Update #14473.

Change-Id: I450d9f51fd280da91952008cd917b749d88960a3
Reviewed-on: https://go-review.googlesource.com/20210
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>