[clang] [ExposeObjCDirect] Adding a flag to expose symbols with objc_direct (PR #170616)

[Tarun Prabhu via cfe-commits]

https://github.com/tarunprabhu requested changes to this pull request.

I have only reviewed the driver-related code. I cannot comment on anything else.

https://github.com/llvm/llvm-project/pull/170616