As an update to the build instructions for the latest version changing the structure slightly, you must now declare vtterminal and picocalcdisplay as separate user modules, it just changed the cmake arguments slightly.
Updated command would be something like:
cmake .. -DUSER_C_MODULES="/absolute/path/to/PicoCalc-Micropython-driver/picocalcdisplay/micropython.cmake;/absolute/path/to/PicoCalc-Micropython-driver/vtterminal/micropython.cmake;/absolute/path/to/micropython-cppmem/micropython.cmake" -DMICROPY_BOARD=PIMORONI_PICO_PLUS2
make
Just be careful, it is case sensitive and I could’ve typed this post up wrong.