Now that -m64 + LLD + MINGW works, the question is obvious.
The background idea is of course to allow the use of GDB under Windows. At first glance the debug info API is not uniform. This is visible if you compare dmd.backend.dwarf and dmd.backend.cgcv and the naive idea which would be to replace all the calls starting with 'cv8_' with their "dwarf_" equivalent won't work (let's say to test in a first time, later a new compiler switch could be added to select the debug info format).
