to align with targets that have made the transition.

We introduced VariantKinds after MCSymbolRefExpr::VariantKind and then
deprecated the VariantKind naming in favor of AtSpecifier (#133214).
Rename the function and type to use the recommended convention.

Move wasm-specific members outside of MCSymbolRefExpr::VariantKind (a
legacy interface I am eliminating). Most changes are mechanic and
similar to what I've done for many ELF targets (e.g. X86 #132149)

Notes:

* `fixSymbolsInTLSFixups` is replaced with `setTLS` in
  `WebAssemblyWasmObjectWriter::getRelocType`, similar to what I've done
  for many ELF targets.
* `SymA->setUsedInGOT()` in `recordRelocation` is moved to
  `getRelocType`.

While here, rename "Modifier' to "Specifier":

> "Relocation modifier", though concise, suggests adjustments happen during the linker's relocation step rather than the assembler's expression evaluation. I landed on "relocation specifier" as the winner. It's clear, aligns with Arm and IBM’s usage, and fits the assembler's role seamlessly.

Pull Request: https://github.com/llvm/llvm-project/pull/133116

Follow-up to 14951a5a3120e50084b3c5fb217e2d47992a24d1

* Unify getVariantKindName and getVariantKindForName
* Allow each target to specify the preferred case (albeit ignored in MCParser)

Note: targets that use variant kinds should call MCExpr::print with a
non-null MAI to print variant kinds. operator<< passes a nullptr to
`MCExpr::print`, which should be avoided (e.g. Hexagon; fixed in
commit cf00ac81ac049cddb80aec1d6d88b8fab4f209e8).

Following discussions in #110443, and the following earlier discussions
in https://lists.llvm.org/pipermail/llvm-dev/2017-October/117907.html,
https://reviews.llvm.org/D38482, https://reviews.llvm.org/D38489, this
PR attempts to overhaul the `TargetMachine` and `LLVMTargetMachine`
interface classes. More specifically:
1. Makes `TargetMachine` the only class implemented under
`TargetMachine.h` in the `Target` library.
2. `TargetMachine` contains target-specific interface functions that
relate to IR/CodeGen/MC constructs, whereas before (at least on paper)
it was supposed to have only IR/MC constructs. Any Target that doesn't
want to use the independent code generator simply does not implement
them, and returns either `false` or `nullptr`.
3. Renames `LLVMTargetMachine` to `CodeGenCommonTMImpl`. This renaming
aims to make the purpose of `LLVMTargetMachine` clearer. Its interface
was moved under the CodeGen library, to further emphasis its usage in
Targets that use CodeGen directly.
4. Makes `TargetMachine` the only interface used across LLVM and its
projects. With these changes, `CodeGenCommonTMImpl` is simply a set of
shared function implementations of `TargetMachine`, and CodeGen users
don't need to static cast to `LLVMTargetMachine` every time they need a
CodeGen-specific feature of the `TargetMachine`.
5. More importantly, does not change any requirements regarding library
linking.

cc @arsenm @aeubanks

WebAssemblyUtils depends on CodeGen which depends on all middle end
optimization libraries.

This component is used by WebAssembly's AsmParser, Disassembler, and
MCTargetDesc libraries. Because of this, any MC layer tool built with
WebAssembly support includes a larger portion of LLVM than it should.

To fix this I've created an MC only version of WebAssemblyTypeUtilities.cpp
in MCTargetDesc to be used by the MC components.

This shrinks llvm-objdump and llvm-mc on my local release+asserts
build by 5-6 MB.

Reviewed By: MaskRay, aheejin

Differential Revision: https://reviews.llvm.org/D144354

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.

IAS has been enabled on WebAssembly since commit 0a55d3f557a74cfb459b24e442072302d5444baf.

This supports bitcode compilation using `clang -fwasm-exceptions`.

---

The current situation:

Currently the backend requires two options for Wasm EH:
`-wasm-enable-eh` and `-exception-model=wasm`. Wasm SjLj requires two
options as well: `-wasm-enable-sjlj` and `-exception-model=wasm`. When
using Wasm EH via Emscripten, you only need to pass `-fwasm-exceptions`,
and these options will be added within the clang driver. This
description will focus on the case of Wasm EH going forward, but Wasm
SjLj's case is similar.

When you pass `-fwasm-exceptions` to emcc and clang driver, the clang
driver adds these options to the command line that calls the clang
frontend (`clang -cc1`): `-mllvm -wasm-enable-eh` and
`-exception-model=wasm`. `-wasm-enable-eh` is prefixed with `-mllvm`, so
it is passed as is to the backend. But `-exception-model` is parsed and
processed within the clang frontend and stored in `LangOptions` class.
This info is later transferred to `TargetOptions` class, and then
eventually passed to `MCAsmInfo` class. All LLVM code queries this
`MCAsmInfo` to get the exception model.

---

Problem:

The problem is the whole `LangOptions` processing is bypassed when
compiling bitcode, so the information transfer of `LangOptions` ->
`TargetOptions` -> `MCAsmInfo` does not happen. They are all set to
`ExceptionHandling::None`, which is the default value.

---

What other targets do, and why we can't do the same:

Other targets support bitcode compilation by the clang driver, but they
can do that by using different triples. For example, X86 target supports
multiple triples, each of which has its own subclass of `MCAsmInfo`, so
it can hardcode the appropriate exception model within those subclasses'
constructors. But we don't have separate triples for each exception
mode: none, emscripten, and wasm.

---

What this CL does:

If we can figure out whether `-wasm-enable-eh` is passed to the backend,
we can programatically set the exception model from the backend, rather
than requiring it to be passed.

So we check `WasmEnableEH` and `WasmEnableSjLj` variables, which are
`cl::opt` for `-wasm-enable-eh` and `-wasm-enable-sjlj`, in
`WebAssemblyMCAsmInfo` constructor, and if either of them is set, we set
`MCAsmInfo.ExceptionType` to Wasm. `TargetOptions` cannot be updated
there, so we make sure they are the same later.

Fixes https://github.com/emscripten-core/emscripten/issues/15712.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D115893

Needed for wasm64, see discussion in https://reviews.llvm.org/D91203

Differential Revision: https://reviews.llvm.org/D91395