I use Macports for GnuRadio dependencies on OS X. For itpp see https://www.macports.org/ports.php?by=name&substr=itpp
Install Macports (if you want to use it). then 'sudo port install itpp’, Macports will install itpp’s dependancy for fftw-3. You can also 'sudo port install gnuradio’. But before anyone installs via Macports make sure to uninstall same packages installed from/by other means to avoid conflicts. Dom