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

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> 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

FWIW, I continuously build and test LLVM (both running LLVM itself on, and generating code for) on 32 bit Windows targets, both i386 and arm.

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