custom cc script: Use gcc46's c++ library instead of base

custom cc script: Use gcc46's c++ library instead of base

There will be a slight performance hit with having to make two calls to
gnatc++ before every real call in order to use gnat-aux's c++ library
rather than the base systems gcc 4.4 c++ library.  The alternative is
hardcoding these values as a function of arch which is less appealing.