[RFA/c++] Fix printing classes with virtual base classes

[Andrew Cagney]

> I don't have any comments on Daniel's patch, but I am wondering who
> will approve this.  Given that we currently have no C++ maintainer,
> should we treat Daniel's patch as an RFC and have him commit it after
> a few days if there are no objections?

I'm pretty sure Jim Blandy, as a (most experienced?) language 
maintainer, will take care of it.

Andrew