tlsdate: add openat to seccomp

This adds openat to a seccomp policy file if open is already there.
We need this because glibc 2.25 changed it system call for open().

BUG=chromium:894614
TEST=None

Change-Id: I9543567547a326adb2d435a9ced9e8b58d56e957
Reviewed-on: https://chromium-review.googlesource.com/1291874
Commit-Ready: Yunlian Jiang <yunlian@chromium.org>
Tested-by: Yunlian Jiang <yunlian@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
3 files changed