Introduce symbol versioning for clang-cpp (#116556)
The situation that required symbol versions on the LLVM shared library
can also happen for clang-cpp, although it is less common: different
tools require different versions of the library, and through transitive
dependencies a process ends up with multiple copies of clang-cpp. This
causes havoc with ELF, because calls meant to go one version of the
library end up with another.
I've also considered introducing a symbol version globally, but for
example the clang (C) library and other targets outside of LLVM/Clang,
e.g. libc++, would not want that. So it's probably best if we keep it to
those libraries.
