[clang] [clang][DebugInfo] Make fwd decl call site debug info consistent for methods (PR #222263)

[Orlando Cazalet-Hyams via cfe-commits]

OCHyams wrote:

How does the comment sound?

> Would it make sense to push this logic into EmitFunctionDecl, or is that too complicated?

hrrrm, honestly I'm not sure, being not massively familiar with all the front end machinery. I had a quick look and it's probably ok to do that. However, I would naturally err on the side of keeping the change localised (as it is now) as I'm not confident. I can investigate more if you feel it's worth it though 

https://github.com/llvm/llvm-project/pull/222263