Add "unconditional errno" support to syscall filter policies.

BUG=chromium:224082
TEST=syscall_filter_unittest

Change-Id: Ic83ecb72af8b62f297f1b6a3dc49eb3219029715
Reviewed-on: https://gerrit.chromium.org/gerrit/46568
Tested-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Commit-Queue: Jorge Lucangeli Obes <jorgelo@chromium.org>
2 files changed