This defines some new target features. These are subsets of existing
features that reflect implementation concerns:

- "call-indirect-overlong" - implied by "reference-types"; just the
overlong encoding for the `call_indirect` immediate, and not the actual
reference types.

- "bulk-memory-opt" - implied by "bulk-memory": just `memory.copy` and
`memory.fill`, and not the other instructions in the bulk-memory
proposal.

This is split out from https://github.com/llvm/llvm-project/pull/112035.

---------

Co-authored-by: Heejin Ahn <aheejin@gmail.com>

This commit implements the [wide-arithmetic] proposal which has recently
reached phase 2 in the WebAssembly proposals process. The goal here is
to implement support in LLVM for emitting these instructions which are
gated behind a new feature flag by default. A new `wide-arithmetic`
feature flag is introduced which gates these four new instructions from
being emitted.

Emission of each instruction itself is relatively simple given LLVM's
preexisting lowering rules and infrastructure. The main gotcha is that
due to the multi-result nature of all of these instructions it needed
the lowerings to be implemented in C++ rather than in TableGen.

[wide-arithmetic]: https://github.com/WebAssembly/wide-arithmetic

This better aligns with how the feature is being referred to and what
runtimes (V8) are calling it.

This currently only defines a constant, but in the future will be used
to gate builtins for experimenting and prototyping half-precision
proposal (https://github.com/WebAssembly/half-precision).

Adding to allow users to get this flag into the target features section for
future use cases.

Reviewed By: tlively, aheejin

Differential Revision: https://reviews.llvm.org/D158409

Move WebAssemblyUtilities from Utils to the CodeGen library. It
primarily deals in MIR layer types, so it really lives in the CodeGen
library.

Move a variety of other things around to try create better separation.

See issue #64166 for more info on layering.

Move llvm/include/CodeGen/WasmAddressSpaces.h back to
llvm/lib/Target/WebAssembly/Utils.

Differential Revision: https://reviews.llvm.org/D156472

We don't yet do anything when this feature is enabled, this change
just lays the ground work by accepting that there is such a feature.

See https://github.com/WebAssembly/extended-const

Differential Revision: https://reviews.llvm.org/D121151

This currently only defines a constant, but it the future will be used
to gate builtins for experimenting and prototyping relaxed-simd proposal
(https://github.com/WebAssembly/relaxed-simd/).

Differential Revision: https://reviews.llvm.org/D110111