The 256-bit maximum vector register size control was removed from AVX10
whitepaper, ref: https://cdrdv2.intel.com/v1/dl/getContent/784343

We have warned these options in LLVM21 through #132542. This patch
removes underlying implementations in LLVM22.

## Purpose

This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the `llvm-c` interface with a
new `LLVM_C_ABI` annotation, which behaves like the `LLVM_ABI`. This
annotation currently has no meaningful impact on the LLVM build;
however, it is a prerequisite to support an LLVM Windows DLL (shared
library) build.

## Overview

1. Add a new `llvm-c/Visibility.h` header file that defines a new
`LLVM_C_ABI` macro. The macro resolves to the proper DLL export/import
annotation on Windows and a "default" visibility annotation elsewhere.
2. Add a new `LLVM_ENABLE_LLVM_C_EXPORT_ANNOTATIONS` `#cmakedefine` that
is used to gate the definition of `LLVM_C_ABI`.
3. Remove the existing `LLVM_C_ABI` definition from
`llvm/Support/Compiler.h`. Update the small number of `LLVM_C_ABI`
references to get it from the new `llvm-c/Visibility.h` header.
4. Code-mod annotate the public `llvm-c` interface using the [Interface
Definition Scanner (IDS)](https://github.com/compnerd/ids) tool.
5. Format the changes with `clang-format`.

## Background

This effort is tracked in #109483. Additional context is provided in
[this
discourse](https://discourse.llvm.org/t/psa-annotating-llvm-public-interface/85307),
and documentation for `LLVM_ABI` and related annotations is found in the
LLVM repo
[here](https://github.com/llvm/llvm-project/blob/main/llvm/docs/InterfaceExportAnnotations.rst).

## Validation

Local builds and tests to validate cross-platform compatibility. This
included llvm, clang, and lldb on the following configurations:

- Windows with MSVC
- Windows with Clang
- Linux with GCC
- Linux with Clang
- Darwin with Clang

In `X86MCTargetDesc.cpp` while fixing the handling of UEFI target in the
`createX86MCAsmInfo` function (#132461), the previous incorrect handling
of isUEFI was not removed. This patch cleans up that case.

For UEFI targets use Microsoft masm.

It allows access to subtarget features, collected in llvm-objdump.cpp,
from findPltEntries, which will be used in
https://github.com/llvm/llvm-project/pull/130764.

Identified with misc-include-cleaner.

Switch LLVMInitialize* functions to new the symbol visibility macros
that will work for windows.
This is part of the work to enable LLVM_BUILD_LLVM_DYLIB and plugins on
windows.

https://reviews.llvm.org/D70157 (for Intel Jump Conditional Code
Erratum) introduced two virtual function calls in the generic
MCObjectStreamer::emitInstruction, which added some overhead.

This patch removes the virtual function overhead:

* Define `llvm::X86_MC::emitInstruction` that calls `emitInstruction{Begin,End}`.
* Define {X86ELFStreamer,X86WinCOFFStreamer}::emitInstruction to call `llvm::X86_MC::emitInstruction`

Pull Request: https://github.com/llvm/llvm-project/pull/96835