minijail: Add named constants for seccomp filters

This makes it possible to write filters using named constants (like
ENOSYS instead of 38).

BUG=chromium:516701
TEST=syscall_filter_unittest passes.

Change-Id: Ic44cbdfb6f2228f6f658b1cc48adf5a923394306
Reviewed-on: https://chromium-review.googlesource.com/290540
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Trybot-Ready: Luis Hector Chavez <lhchavez@google.com>
Tested-by: Luis Hector Chavez <lhchavez@google.com>
Commit-Queue: Luis Hector Chavez <lhchavez@google.com>
7 files changed