`std::aligned_storage` is deprecated with C++23, see
[here](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p1413r3.pdf).

This replaces the usages of `std::aligned_storage` within llvm (only one
in ADT and one in Support) with an aligned `std::byte` array.
I will provide patches for other subcomponents as well.

ATOMIC_VAR_INIT has a trivial definition `#define ATOMIC_VAR_INIT(value) (value)`,
is deprecated in C17/C++20, and will be removed in newer standards.

The cleanup was manual, but assisted by "include-what-you-use". It consists in

1. Removing unused forward declaration. No impact expected.
2. Removing unused headers in .cpp files. No impact expected.
3. Removing unused headers in .h files. This removes implicit dependencies and
   is generally considered a good thing, but this may break downstream builds.
   I've updated llvm, clang, lld, lldb and mlir deps, and included a list of the
   modification in the second part of the commit.
4. Replacing header inclusion by forward declaration. This has the same impact
   as 3.

Notable changes:

- llvm/Support/TargetParser.h no longer includes llvm/Support/AArch64TargetParser.h nor llvm/Support/ARMTargetParser.h
- llvm/Support/TypeSize.h no longer includes llvm/Support/WithColor.h
- llvm/Support/YAMLTraits.h no longer includes llvm/Support/Regex.h
- llvm/ADT/SmallVector.h no longer includes llvm/Support/MemAlloc.h nor llvm/Support/ErrorHandling.h

You may need to add some of these headers in your compilation units, if needs be.

As an hint to the impact of the cleanup, running

clang++ -E  -Iinclude -I../llvm/include ../llvm/lib/Support/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l

before: 8000919 lines
after:  7917500 lines

Reduced dependencies also helps incremental rebuilds and is more ccache
friendly, something not shown by the above metric :-)

Discourse thread on the topic: https://llvm.discourse.group/t/include-what-you-use-include-cleanup/5831

Fixes some clang-tidy warnings.

A common routine is to have the compiler crash, and attempt to rerun the
cc1 command-line by copying and pasting the arguments printed by
`llvm::Support::PrettyStackProgram::print`. However, these arguments are
not quoted or escaped which means they must be manually edited before
working correctly. This patch ensures that shell-unfriendly characters
are C-escaped, and arguments with spaces are double-quoted reducing the
frustration of running cc1 inside a debugger.

As the quoting is C, this is "best effort for most shells", but should
be fine for at least bash, zsh, csh, and cmd.exe.

Reviewed by: jhenderson

Differential Revision: https://reviews.llvm.org/D90759

Commit a945037e8fd0c30e250a62211469eea6765a36ae moved the printing of the
"PLEASE submit a bug report" message to the crash handler, but that means we
don't print it when forcing a crash using FORCE_CLANG_DIAGNOSTICS_CRASH. Fix
this by adding a function to get the bug report message and printing it when
forcing a crash.

Differential Revision: https://reviews.llvm.org/D81672

Fixes a build break with LLVM_ENABLE_BACKTRACES=OFF.

Differential Revision: https://reviews.llvm.org/D76893

When Clang crashes a useful message is output:

"PLEASE submit a bug report to https://bugs.llvm.org/ and include the
crash backtrace, preprocessed source, and associated run script."

A similar message is now output for all tools.

Differential Revision: https://reviews.llvm.org/D74324