This patch migrates uses of StringRef::{starts,ends}with_insensitive
to StringRef::{starts,ends}_with_insensitive so that we can use names
similar to those used in std::string_view.

Note that the llvm/ directory has migrated in commit
6c3ea866e93003e16fc55d3b5cedd3bc371d1fde.

I'll post a separate patch to deprecate
StringRef::{starts,ends}with_insensitive.

Differential Revision: https://reviews.llvm.org/D150506

Differential Revision: https://reviews.llvm.org/D137799

The forwarding header is left in place because of its use in
`polly/lib/External/isl/interface/extract_interface.cc`, but I have
added a GCC warning about the fact it is deprecated, because it is used
in `isl` from where it is included by Polly.

I also ran `git clang-format` to get the headers in the right order for
the new location, which has changed the order of other headers in two
files.

The commit transitively includes lld/include/lld/Common/ErrorHandler.h into
lld/include/lld/Common/Driver.h, which is not intended.

This is a fairly large changeset, but it can be broken into a few
pieces:
- `llvm/Support/*TargetParser*` are all moved from the LLVM Support
  component into a new LLVM Component called "TargetParser". This
  potentially enables using tablegen to maintain this information, as
  is shown in https://reviews.llvm.org/D137517. This cannot currently
  be done, as llvm-tblgen relies on LLVM's Support component.
- This also moves two files from Support which use and depend on
  information in the TargetParser:
  - `llvm/Support/Host.{h,cpp}` which contains functions for inspecting
    the current Host machine for info about it, primarily to support
    getting the host triple, but also for `-mcpu=native` support in e.g.
    Clang. This is fairly tightly intertwined with the information in
    `X86TargetParser.h`, so keeping them in the same component makes
    sense.
  - `llvm/ADT/Triple.h` and `llvm/Support/Triple.cpp`, which contains
    the target triple parser and representation. This is very intertwined
    with the Arm target parser, because the arm architecture version
    appears in canonical triples on arm platforms.
- I moved the relevant unittests to their own directory.

And so, we end up with a single component that has all the information
about the following, which to me seems like a unified component:
- Triples that LLVM Knows about
- Architecture names and CPUs that LLVM knows about
- CPU detection logic for LLVM

Given this, I have also moved `RISCVISAInfo.h` into this component, as
it seems to me to be part of that same set of functionality.

If you get link errors in your components after this patch, you likely
need to add TargetParser into LLVM_LINK_COMPONENTS in CMake.

Differential Revision: https://reviews.llvm.org/D137838

This is part of an effort to migrate from llvm::Optional to
std::optional:

https://discourse.llvm.org/t/deprecating-llvm-optional-x-hasvalue-getvalue-getvalueor/63716

Previously the response file expansion code would print the error, but
lld would not exit, which was odd.

lld does response file expansion in the different drivers, but it's also
done in main() first, so it's enough to check there.

By checking for these errors we would have caught when D136090
introduced a bug that made lld print errors for response files which
contained "-rpath @foo".

Differental revision: https://reviews.llvm.org/D137477

The llvm-driver, enabled with LLVM_TOOL_LLVM_DRIVER_BUILD combines many llvm executables
into one to save overall toolchain size. This patch adds the capability for lld to be part of the
llvm-driver.

Differential Revision: https://reviews.llvm.org/D127472

Add FORCE_LLD_DIAGNOSTICS_CRASH inspired by the existing
FORCE_CLANG_DIAGNOSTICS_CRASH.

This is particularly useful for people customizing LLD as they may
want to modify the crash reporting behavior.

Differential Revision: https://reviews.llvm.org/D128195