I have realised this is an error on my part - I was compiling the master branch. For others wanting to use the command line tools, the following steps worked for me:
sudo apt install gfortran
git clone GitHub - emlid/RTKLIB: Emlid's fork of Tomoji Takasu's RTKLIB used in Reach RTK receiver
git checkout reach
make -j
make mkdir
sudo make install
sudo ldconfig
Kind Regards