I ready to work under this. I suggest the next roadmap:
1. You introduce mangling interface in this PR (It can be simple `cppMangleOf(Dsymbol *)` function or something else). 
2. I merge current GCC C++ mangling with my work (@ibuclaw has made some changes since my last activity in #2074).
3. I move Win32 C++ mangling to frontend.

Ok?