tar -xvf fftw-3.3.8.tar.gz
cd fftw-3.3.8
export CC=`which clang` export CXX=`which clang++` export FC=`which flang`
./bootstrap.sh
./configure --prefix=/path/to/FFTW --enable-threads --enable-float
make make install
export PATH=/path/to/FFTW/bin:$PATH export LD_LIBRARY_PATH=/path/to/FFTW/lib:$LD_LIBRARY_PATH