This is required for GCC which uses libcalls for outlined atomics.

Reviewed by:	dim
Differential Revision:	https://reviews.freebsd.org/D55157

In commit 2e47f35be5dc libllvm, libclang and liblldb were converted into
private shared libraries. This allowed clang, lld, lldb, and other llvm
tools to be linked against these shared libraries, which makes them
smaller and avoids duplication.

However, this also comes at the cost of some performance, since the
dynamic libraries are quite large, and contain lots of long symbols
(mangled C++ identifiers).

Add a WITH_LLVM_LINK_STATIC_LIBRARIES build knob that can be used to go
back to the previous behavior: libllvm, libclang and liblldb are built
as internal static libraries, i.e. only available during buildworld, and
fully linked into the various executables such as clang, lld, etc.

PR:		287447
Reviewed by:	emaste
MFC after:	1 week
Differential Revision: https://reviews.freebsd.org/D50956

clang-scan-deps is used to generate dependency information from C++20
modules according to proposed standard ISO/IEC WG21 P1689R5[0].  It is
required by common build tools (e.g., CMake) to build C++ sources
that use modules.

Since this is a core build tool, install it by default, not gated
behind MK_CLANG_EXTRAS.

[0] https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2022/p1689r5.html

MFC after:	3 days
Reviewed by:	kevans, dim
Approved by:	kevans (mentor)
Requested by:	jbo
Differential Revision:	https://reviews.freebsd.org/D51044

This allows clang, lld, lldb, and other llvm tools to be linked against
these shared libraries, which makes them smaller and avoids duplication.

Since these are not quite the same as the shared libraries shipped by
the upstream llvm build system, and we do not want to expose the ABI to
external programs such as ports, make them private libraries.

Note that during the cross-tools stage they are still built as static
libraries, so the cross compiler and linker are static binaries, as they
have always been.

This also requires a depend-cleanup.sh kludge which will be added in a
follow-up commit, to ensure binaries are rebuilt against the shared
libraries in case of incremental builds.

MFC after:      2 weeks
Differential Revision: https://reviews.freebsd.org/D49967

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project release/19.x llvmorg-19.1.0-rc1-0-ga4902a36d5c2.

PR:		280562
MFC after:	1 month

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-19-init-18630-gf2ccf80136a0, the
last commit before the upstream release/19.x branch was created.

PR:		280562
MFC after:	1 month

This is a residual of the $FreeBSD$ removal.

MFC After: 3 days (though I'll just run the command on the branches)
Sponsored by: Netflix

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-18359-g93248729cfae, the
last commit before the upstream release/18.x branch was created.

PR:		276104
MFC after:	1 month

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-15692-g007ed0dccd6a.

PR:		276104
MFC after:	1 month

This updates llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and
openmp to llvm-project main llvmorg-18-init-15088-gd14ee76181fb.

PR:		276104
MFC after:	1 month