Remove $FreeBSD$: one-line sh pattern

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

build: provide a default WARNS for all in-tree builds

The current default is provided in various Makefile.inc in some top-level
directories and covers a good portion of the tree, but doesn't cover parts
of the build a little deeper (e.g. libcasper).

Provide a default in src.sys.mk and set WARNS to it in bsd.sys.mk if that
variable is defined. This lets us relatively cleanly provide a default WARNS
no matter where you're building in the src tree without breaking things
outside of the tree.

Crunchgen has been updated as a bootstrap tool to work on this change
because it needs r365605 at a minimum to succeed. The cleanup necessary to
successfully walk over this change on WITHOUT_CLEAN builds has been added.

There is a supplemental project to this to list all of the warnings that are
encountered when the environment has WARNS=6 NO_WERROR=yes:
https://warns.kevans.dev -- this project will hopefully eventually go away
in favor of CI doing a much better job than it.

Reviewed by: emaste, brooks, ngie (all earlier version)
Reviewed by: emaste, arichardson (depend-cleanup.sh change)
Differential Revision: https://reviews.freebsd.org/D26455

Merge ^/user/ngie/release-pkg-fix-tests to unbreak how test files are installed
after r298107

Summary of changes:

- Replace all instances of FILES/TESTS with ${PACKAGE}FILES. This ensures that
namespacing is kept with FILES appropriately, and that this shouldn't need
to be repeated if the namespace changes -- only the definition of PACKAGE
needs to be changed
- Allow PACKAGE to be overridden by callers instead of forcing it to always be
`tests`. In the event we get to the point where things can be split up
enough in the base system, it would make more sense to group the tests
with the blocks they're a part of, e.g. byacc with byacc-tests, etc
- Remove PACKAGE definitions where possible, i.e. where FILES wasn't used
previously.
- Remove unnecessary TESTSPACKAGE definitions; this has been elided into
bsd.tests.mk
- Remove unnecessary BINDIRs used previously with ${PACKAGE}FILES;
${PACKAGE}FILESDIR is now automatically defined in bsd.test.mk.
- Fix installation of files under data/ subdirectories in lib/libc/tests/hash
and lib/libc/tests/net/getaddrinfo
- Remove unnecessary .include <bsd.own.mk>s (some opportunistic cleanup)

Document the proposed changes in share/examples/tests/tests/... via examples
so it's clear that ${PACKAGES}FILES is the suggested way forward in terms of
replacing FILES. share/mk/bsd.README didn't seem like the appropriate method
of communicating that info.

MFC after: never probably
X-MFC with: r298107
PR: 209114
Relnotes: yes
Tested with: buildworld, installworld, checkworld; buildworld, packageworld
Sponsored by: EMC / Isilon Storage Division

First pass to fix the 'tests' packages.

Sponsored by: The FreeBSD Foundation

Fix LDADD/DPADD that should be LIBADD.

Sponsored by: EMC / Isilon Storage Division

Refactor the test/ Makefiles after recent changes to bsd.test.mk (r289158) and
netbsd-tests.test.mk (r289151)

- Eliminate explicit OBJTOP/SRCTOP setting
- Convert all ad hoc NetBSD test integration over to netbsd-tests.test.mk
- Remove unnecessary TESTSDIR setting
- Use SRCTOP where possible for clarity

MFC after: 2 weeks
Sponsored by: EMC / Isilon Storage Divison

Add reachover Makefiles for contrib/netbsd-tests/lib/libpthread as
lib/libthr/tests

A variant of this code has been tested on amd64/i386 for some time by
EMC/Isilon on 10-STABLE/11-CURRENT. It builds on other architectures, but the
code will remain off until it's proven it works on virtual hardware or real
hardware on other architectures

Original work by: pho
Sponsored by: EMC / Isilon Storage Division