Old Linux distributions requirements

For Debian 9 and Ubuntu 16.04, you need to install a recent version of libmpfr to use the hermit toolchain:

wget https://www.mpfr.org/mpfr-current/mpfr-4.0.2.tar.bz2
tar xf mpfr-4.0.2.tar.bz2
cd mpfr-4.0.2
./configure
make -j`nproc`
sudo make install
sudo ldconfig

For Ubuntu 16.04 you need a recent version of cmake:

# It is probably better to uninstall any existing installation:
sudo apt remove cmake
wget https://github.com/Kitware/CMake/releases/download/v3.14.3/cmake-3.14.3.tar.gz
tar xf cmake-3.14.3.tar.gz
cd cmake-3.14.3
./configure
make -j`nproc`
sudo make install