[llvm] annotate ABIBreakingChecks symbols for DLL export (#145575)

## Purpose
This patch is one in a series of code-mods that annotate LLVM’s public
interface for export. This patch annotates the ABI Breaking Checks
interface in llvm/config. The annotations currently have no meaningful
impact on the LLVM build; however, they are a prerequisite to support an
LLVM Windows DLL (shared library) build.

## Background
The effort to build LLVM as a Windows DLL 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

0 files changed, 0 insertions, 0 deletions