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

[John McCall via cfe-commits]

https://github.com/rjmccall commented:

I'm not sure how I feel about this use of "expose" to specifically mean "don't put the prefix byte on it". What linkage and visibility do these end up getting?

The patch otherwise seems fine.

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