[llvm] [Support][Windows] Silence warnings when retrieving DLL-exported functions (PR #97905)

[Saleem Abdulrasool via llvm-commits]

https://github.com/compnerd approved this pull request.

I see, the `void*` is an intermediate cast to drop the `FARPROC`. That seems fine to me. The one final piece - the function is type erased irrespective of windows or not and DLL exported or not. Symbols on ELF and MachO libraries will also be "type erased".

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