Follow CL 74952 for x/sys/unix.

Update golang/go#22528

Change-Id: Id146da75b80a64cfa4eac28e9bb7b3befe944718
Reviewed-on: https://go-review.googlesource.com/75610
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>