CL 159859 causes build failure with old clang versions (3.4.1) on FreeBSD 10.3/10.4.

Update #29962
Update #27619

Change-Id: I78264ac5d8d17eeae89a982e89aac988eb22b286
Reviewed-on: https://go-review.googlesource.com/c/160777
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>