Pick up the changes from CL 114395, CL 114396 and CL 114415.

By re-running govendor in the latest version, some files from
golang.org/x/sys/unix which are ignored for the build also got removed
from the vendored copy.

Updates #25528
Updates #25535

Change-Id: I5c0002fc3a37d6abaafed2e15cc3e2ade803ad7b
Reviewed-on: https://go-review.googlesource.com/114416
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>