[llvm] [MSVC][Demangling] Respect MSDF_NoCallingConvention for function pointers (PR #209113)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

I don't feel like I have the expertise to review this with any confidence, so hopefully @rnk can help out. Alternatively, maybe the @llvm/llvm-area-team can help identify reviewers?

https://github.com/llvm/llvm-project/pull/209113