Remove $FreeBSD$: one-line sh pattern

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

remove GCC 4.2.1 build infrastructure

As described in Warner's email message[1] to the FreeBSD-arch mailing
list we have reached GCC 4.2.1's retirement date. At this time all
supported architectures either use in-tree Clang, or rely on external
toolchain (i.e., a contemporary GCC version from ports).

GCC 4.2.1 was released July 18, 2007 and was imported into FreeBSD later
that year, in r171825. GCC has served us well, but version 4.2.1 is
obsolete and not used by default on any architecture in FreeBSD. It
does not support modern C and does not support arm64 or RISC-V.

Thanks to everyone responsible for maintaining, updating, and testing
GCC in the FreeBSD base system over the years.

So long, and thanks for all the fish.

[1] https://lists.freebsd.org/pipermail/freebsd-arch/2020-January/019823.html

PR: 228919
Reviewed by: brooks, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D23124

META MODE: Fix 'make bootstrap-tools'.

The main problem was bitrot after elftoolchain being swapped in for the
GNU toolchain.

This also reworks how the list of 'host allowed' libraries is determined
to only allow INTERNALLIBs, which is needed for libelftc to come in.

For usr.bin/readelf use the same hack, as libelf and libdward, to bring in
the needed sys/ headers for host builds. This has not yet been a problem due
to readelf not being built as a host tool in buildworld. This is possible
in the meta build though when building the toolchain.

Sponsored by: EMC / Isilon Storage Division

META_MODE: Remove DEP_RELDIR from Makefile.depend files.

This has not been needed since r284171 in projects/bmake.

Sponsored by: EMC / Isilon Storage Division

Roll WITHOUT_ELFTOOLCHAIN_TOOLS into WITHOUT_TOOLCHAIN

The option was added only to ease the transition from GNU Binutils to
ELF Tool Chain tools, and that process is now complete (for the viable
replacements). Noting the removal in UPDATING is sufficient as we have
not shipped a release with the option.

Reviewed by: brooks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D3240

Support WITH_LLDB

Remove entries from userland/gnu that conflict with toolchain

Pay attention to MK_ELFTOOLCHAIN_TOOLS so we build the desired tools.

Renamed pkgs/ targets/

Rename pkgs to more generic targets (that's what they are)

Reviewed by: marcel