[llvm] [llvm] export private symbols needed by unittests (PR #145767)

[Saleem Abdulrasool via llvm-commits]

compnerd wrote:

I wonder if we should track these somehow? Since we will have some path towards a more formal definition of the API surface that is needed as ABI for the tools, we could work from there to a future where we can maintain source compatibility at least (C++ is not the best language for ABI stability).

https://github.com/llvm/llvm-project/pull/145767