[llvm] [Support][Windows] Add utility function for retrieving a DLL-exported function (PR #97905)

[Saleem Abdulrasool via llvm-commits]

https://github.com/compnerd commented:

This is confusing to me. I think that we should declare typedefs for the function pointer type. I doubt that anyone wants to build on 32-bit at this point, but the calling convention differences on Windows really do require that we create typedefs for the function pointer type so that we can account for the calling convention.

https://github.com/llvm/llvm-project/pull/97905