MFC r334360, r334362, r334388, r334395

r334360:
Add initial set of tests for audit(4)

This change includes the framework for testing the auditability of various
syscalls, and includes changes for the first 12. The tests will start
auditd(8) if needed, though they'll be much faster if it's already running.
The syscalls tested in this commit include mkdir(2), mkdirat(2), mknod(2),
mknodat(2), mkfifo(2), mkfifoat(2), link(2), linkat(2), symlink(2),
symlinkat(2), rename(2), and renameat(2).

Submitted by: aniketp
Sponsored by: Google, Inc (GSoC 2018)
Differential Revision: https://reviews.freebsd.org/D15286

r334362 by emaste:
Temporarily disconnect audit tests

Audit tests added in r334360 broke the build on a number of archs.
Remove the subdir from the top level tests/sys/Makefile until they're
fixed.

r334388:
Fix OpenBSM with GCC with -Wredundant-decls

Upstream change ed47534 consciously added some redundant functional
declarations, and I'm not sure why. AFAICT they were never required. On
FreeBSD, they break the build with GCC (but not Clang) for any program
including libbsm.h with WARNS=6.

Fix by cherry-picking upstream change
https://github.com/openbsm/openbsm/commit/0553c27

Reported by: emaste
Reviewed by: cem
Obtained from: OpenBSM
Pull Request: https://github.com/openbsm/openbsm/pull/31

r334395:
Revert r334362

Reconnect tests/sys/audit now that the GCC issue is fixed by 334388

X-MFC-With: 334362, 334360, 334388