The function was duplicated for Solaris. Reuse the BSD version instead.

Change-Id: Ibc812bcf36d21f4a7ceeef7b4fb091fa9479bfa8
Reviewed-on: https://go-review.googlesource.com/81395
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>