[clang] [llvm] Introduce symbol versioning for clang-cpp (PR #116556)

[Aaron Puchert via llvm-commits]

aaronpuchert wrote:

@tstellar, seems like we both overlooked the `if("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")`. Any objections to relanding the patch with that additional condition?

https://github.com/llvm/llvm-project/pull/116556