title: Update gcc alternatives in Ubuntu 18.04 - g++ cannot be slave of gcc
body: <p>Trying to update alternatives but get this error. Googling doesn't show up any solutions.</p>
  <blockquote>
  <p>sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-4.9 60 --slave /usr/bin/g++ g++ /usr/bin/g++-4.9</p>
  <p>update-alternatives: error: alternative g++ can't be slave of gcc: it
  is a master alternative</p>
  </blockquote>