Optionally create full debuginfo for llvm-related executables

Commit de6feefdb7cfd limited the amount of debuginfo generated for clang
and other llvm-related executables. This was done to save disk space and
memory during building, but it makes debugging any of these executables
much harder.

Add a new src.conf(5) setting, WITH_LLVM_FULL_DEBUGINFO, to generate
full debuginfo instead. This is off by default, but could for example be
enabled for release builds or snapshots, so llvm executables are easier
to debug.

Reviewed by: emaste
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43839

Revert "Build clang and other llvm executables as PIE"

This reverts commit 470f9f13de10e47e6d45721c15af6b4abe7aad55.

I need more time to figure out how to make this work correctly with
incremental builds, which it currently miserably fails on.

Build clang and other llvm executables as PIE

There is no reason anymore to not build these as PIE. Unfortunately
bsd.lib.mk does not allow for building _only_ PIE static libraries, so
lib/clang/Makefile.inc needs a kludge to work around that issue.

MFC after: 1 week

pkgbase: Move headers and libs out of runtime and utilities

Headers from src/include were in the runtime-dev package but
subdirectories of src/include ended up in utilities-dev by default.
Neither package is a good choice - the headers in src/include are not
useful without the libraries contained in clibs-dev.

This moves the standard C headers to clibs-dev (C++ headers are already
in this package). While working on this, I found that various clang
libraries and headers were also bundled into utilities-dev by default
so these are also moved to clang-dev.

I also added a FreeBSD-build-essential meta package to make it simple to
install all the toolchain parts.

PR: 254173
Reviewed byb: manu
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D41815

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

Add WITH_PIE knob to build Position Independent Executables

Building binaries as PIE allows the executable itself to be loaded at a
random address when ASLR is enabled (not just its shared libraries).

With this change PIE objects have a .pieo extension and INTERNALLIB
libraries libXXX_pie.a.

MK_PIE is disabled for some kerberos5 tools, Clang, and Subversion, as
they explicitly reference .a libraries in their Makefiles. These can
be addressed on an individual basis later. MK_PIE is also disabled for
rtld-elf because it is already position-independent using bespoke
Makefile rules.

Currently only dynamically linked binaries will be built as PIE.

Discussed with: dim
Reviewed by: kib
MFC after: 1 month
Relnotes: Yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D18423

Improve the coverage of debug symbols for MK_DEBUG_FILES.

- Include debug symbols in static libraries. This permits binaries
to include debug symbols for functions obtained from static libraries.
- Permit the C/C++ compiler flags added for MK_DEBUG_FILES to be
overridden by setting DEBUG_FILES_CFLAGS. Use this to limit the debug
information for llvm libraries and binaries.

Reviewed by: emaste
Sponsored by: DARPA / AFRL
Differential Revision: https://reviews.freebsd.org/D12025