If this looks fine, could you please merge it in? I’m not sure how the merge process is handled for LLVM.

Specify std::string over auto and change message to Msg.

Address review comments by inlining errorOrWarnMultiple.

Could you please either take a look or suggest a reviewer?

Which, I think is just adding something wacky like @swiftcc@__Swift@@ which would demangle as __Swift::swiftcc if the demangler expected an NNS there. Of course, it doesn't, so it won't demangle, but at least you can overload between cdecl and swiftcc then.

Add back a mistakenly removed default case.