Fix C++ demangler in libiberty?

[Benjamin Kosnik]

This is an open wound at the moment. 

I think the correct, long term fix is to take the libstdc++ demangling
code, remove the dependencies, and replace the current libiberty code.
Carlo has done some work along these lines, but I've been pretty swamped
with other review and have been unable to help. I hope to fix this
correctly soon. Would you be willing to help?

-benjamin