unix: add some FreeBSD Capsicum support.

Change-Id: Ibb1426ebd18d27ee9f144af0fd8c94b08c06f7d7
Reviewed-on: https://go-review.googlesource.com/47290
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
11 files changed