Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Explicitly set CXXSTD to c++11 for old C++ code using std::auto_ptr<>.

GCC 12 defaults to C++17 which removes (not just deprecates)
std::auto_ptr<>. Trying to use CXXSTD of c++03 doesn't work with
libc++ headers, but c++11 does.

Reviewed by: brooks, imp, emaste
Differential Revision: https://reviews.freebsd.org/D37531

Fix path to the process_helpers for the libatf-c++ tests.

Because we respect the FreeBSD src tree layout under /usr/tests, and because
the layout of the tests in the atf distfile does not match the former, the
tests for atf-c++ were not able to find the process_helper binary.

Fix this by explicitly hardcoding the right path in the FreeBSD test suite.

Obtained from: atf (git 1f0e878f7f127741a3762883ef24aef317e239d5)
MFC after: 1 week

Build and install the atf tests.

Reviewed by: freebsd-testing
Approved by: rpaulo (mentor)

Add ATF to the build. This is may be a bit rought around the egdes,
but committing it helps to get everyone on the same page and makes
sure we make progress.

Tinderbox breakages that are the result of this commit are entirely
the committer's fault -- in other words: buildworld testing on amd64
only.

Credits follow:

Submitted by: Garrett Cooper <yanegomi@gmail.com>
Sponsored by: Isilon Systems
Based on work by: keramida@
Thanks to: gnn@, mdf@, mlaier@, sjg@
Special thanks to: keramida@