I recently upgraded my Ubuntu 16.04 LTS to a pre-release of Ubuntu 17.10 since it comes with recent compilers. The clang compilers currently create faster binaries than gcc does. Also I wanted to use latest C++ features since I started playing around with libint (electronic integrals library) again.
With a new compiler, I want to be able to easily switch back. Here’s what worked for me:
sudo update-alternatives --install /usr/bin/cc cc /usr/bin/clang-5.0 100
sudo update-alternatives --install /usr/bin/c++ c++ /usr/bin/clang++-5.0 100