How to make D resolve C++ symbols by mangling symbols with the Itanium ABI on Windows

[thumbgun]

I'm currently trying to call some C++ functions that were 
compiled by g++ (mingw). However g++ uses the Itanium ABI name 
mangling rules. dmd on Windows tries to link functions based on 
the MSVC name mangling rules. For example:

```
// add.cpp
int add(int lhs, int rhs)
{
     return lhs + rhs;
}


// main.d
import std.stdio;

extern(C++) int add(int lhs, int rhs);

void main()
{
     auto x = add(5, 6);
     writeln(x);
}


// Command line
g++ add.cpp -c -o add.obj
dmd main.d add.obj


// Output
main.obj : error LNK2019: unresolved external symbol "int __cdecl 
add(int,int)"
(?add@@YAHHH at Z) referenced in function _Dmain

```
The prefix for MSVC symbols is '?' while the Itanium ABI's prefix 
is '_Z'. Is there any way I can make dmd link to symbols mangled 
according to the Itanium ABI's rules on Windows?