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

[Aaron Puchert via cfe-commits]

aaronpuchert wrote:

> LLVM Buildbot has detected a new failure on builder `clang-ppc64-aix` running on `aix-ppc64` while building `clang,llvm` at step 3 "clean-build-dir".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/64/builds/1496
> Here is the relevant piece of the build log for the reference
> 
> ```
> 6343.285 [361/10/4839] Linking CXX shared library lib/libclang-cpp.a
> FAILED: lib/libclang-cpp.a 
> ```

Seems the linker doesn't support the flag, but the CMake configuration log says: "Linker detection: unknown". So how do I detect this case? By detecting AIX?

Maybe @llvm/pr-subscribers-backend-powerpc can help?

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