sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-5 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-5 10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-6 10
sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-7 20
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-6 10
sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-7 20
sudo update-alternatives --config gcc
sudo update-alternatives --config g++
selecting a different gcc the build compiles part but stops immediately
there are solutions