[clang] [llvm] [Clang] Reintroduce obsolete libclang symbols to avoid an ABI break (PR #149079)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

LGTM
This obviously has to be cherry-picked to the release branch.

https://github.com/llvm/llvm-project/pull/149079