Seen on the OpenBSD/AMD64 builder:
https://build.golang.org/log/fa34df1bcd3af12d4fc0fb0e60e3c6197a2a6f75

Update #18146.

Change-Id: I2646621488be84d50f47c312baa0817c72e3c058
Reviewed-on: https://go-review.googlesource.com/33907
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>