add a formula for compiling cryptopp with libstdc++

As described here http://blog.inventic.eu/2014/01/qt-on-osx-maverick-undefined-symbols-for-architecture-x86_64/ you need to compile cryptopp with libstdc++ to include it into a qt project
Here is what I did. I installed qt5 via homebrew. installed qt-creator via homebrew-cask added qt5 inside the creator. Did not change the formulas in any way. A hello world worked fine. I installed cryptopp via homebrew and added it inside creator as external library and got a "Undefined symbols for architecture x86_64", then I found the article from above, I appended the change (of this formula) to the cryptopp formula and it worked. Maybe this should not be a pull request for a new formula, but a issue documenting the problem I had and explaining how to solve it.

As asked I did not upgrade to 10.9 it's a fresh install.