The post is about building GCC itself with a C++ compiler, which is already possible on most(?) platforms: Basically, the default of the --enable-build-with-cxx configuration option will change, which does not affect the default input language of the gcc executable (which is chosen by file extension anyway).

Ah, okay. That I'm fine with. :)

For compiling C++ code. Which gcc will start using. This is just a way to make compiling gcc take 20 times longer.