audit(4): Add tests for setsid(2), wait4(2), wait6(2) and kill(2)

[aniketp]

Summary

This revision introduces atf-c(3) tests for verifying the proper auditability for
syscalls categorized within process-control audit class.
List of syscalls:

• setsid(2)
• wait4(2)
• wait6(2)
• kill(2)

Test Plan

Execute make && make install from test/sys/audit.
Execute kyua test from /usr/tests/sys/audit. All testcases should succeed.

[asomers]

tests/sys/audit/process-control.c

986 ↗

(On Diff #44517)

This assumes too much about Kyua's execution model. You shouldn't assume that it's already a process group leader. For example, if you invoke the test as sudo ./process-control setsid_failure, then it will fail.

[aniketp]

• Call setsid() prematurely to intentionally fail the tests

[asomers]

tests/sys/audit/process-control.c

982 ↗

(On Diff #44536)

This should work. But I would prefer a comment that indicates that we're intentionally ignoring the output of the first setsid call, because we don't know whether we're already a session leader.

[aniketp]

• Update comment explaining why we are ignoring the output of first setsid()