Yes, GCC implements the ABI from the codesourcery link below. As with any spec/doc, I don't know if it is entirely in sync with the latest GCC implementation. I think it makes sense for clang to (eventually) implement this ABI.
Making it configurable is an interesting idea if we actually have another compelling ABI to select. As Seo says, the MS name mangling could be interesting (though I am not aware of any public documentation on it).