dirdeps: Update/fix Makefile.depend* for toolchain

This fixes make pseudo/toolchain.

Remove $FreeBSD$: one-line sh pattern

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

DIRDEPS_BUILD: Update dependencies.

Sponsored by: Dell EMC Isilon

DIRDEPS_BUILD: Connect the new clang build.

Sponsored by: EMC / Isilon Storage Division

Completely revamp the way llvm, clang and lldb are built.

* Bootstrap llvm-tblgen and clang-tblgen with a minimal llvm static
library, that has no other dependencies.
* Roll up all separate llvm libraries into one big static libllvm.
* Similar for all separate clang and lldb static libraries.
* For all these libraries, generate their .inc files only once.
* Link all llvm tools (including extra) against the big libllvm.
* Link clang and clang-format against the big libllvm and libclang.
* Link lldb against the big libllvm, libclang and liblldb.

N.B.: This is work in progress, some details may still be missing.

It also heavily depends on bsd.*.mk's support for SRCS and DPSRCS with
relative pathnames, which apparently does not always work as expected.
For building llvm, clang and lldb though, it seems to work just fine.

The main idea behind this restructuring is maintainability and build
peformance. The previous large number of very small libraries, each
with their own generated files and dependencies was slow to traverse
and hard to understand.

Possible future improvements:
* Only build certain targets, e.g. for most regular users having just
one target will be fine. This will shave off some build time.
* Building the big llvm, clang and lldb libraries as shared (private)
libraries.
* Adding other components from the LLVM project, such as lld.

DIRDEPS_BUILD: Update clang dependencies after r296417.

Sponsored by: EMC / Isilon Storage Division

DIRDEPS_BUILD: Update dependencies.

Sponsored by: EMC / Isilon Storage Division

META MODE: Update dependencies with 'the-lot' and add missing directories.

This is not properly respecting WITHOUT or ARCH dependencies in target/.
Doing so requires a massive effort to rework targets/ to do so. A
better approach will be to either include the SUBDIR Makefiles directly
and map to DIRDEPS or just dynamically lookup the SUBDIR. These lose
the benefit of having a userland/lib, userland/libexec, etc, though and
results in a massive package. The current implementation of targets/ is
very unmaintainable.

Currently rescue/rescue and sys/modules are still not connected.

Sponsored by: EMC / Isilon Storage Division

new depends