This command should provide required packages for FreeBSD installation:
sudo pkg install cmake cython eigen3 harfbuzz opus-tools opusfile png py-numpy py-lz4 py-pillow py-pygments py-toml pylint python qt5 sdl2 sdl2_image
You will also need nyan and its dependencies.
clang is the base compiler however, it is possible to use either any version of gcc>=10 or any other version of clang present in pkg:
sudo pkg install gcc
Select the one to be used by ./configure --help.