On MacOS:
cd native
chmod u+x cppbuild.sh
./cppbuild.sh
cd clij2fft
cd ccpbuild
make
From within IntellIJ: run mvn clean install -DskipTests.
Copy over libclFFT.dylib, libjniclij2fftWrapper.dylib from target/classes/net/..../ to Fiji.app/native/macosx.
Copy over clij2fft.dylib from /native/clij2fft/cppbuild to Fiji.app/native/macosx.