Should fix the clang builder.

Change-Id: I3ee34581b6a7ec902420de72a8a08a2426997782
Reviewed-on: https://go-review.googlesource.com/30363
Run-TryBot: Michael Munday <munday@ca.ibm.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>