Try to use GCC on OSX for OpenMP support.

def set_gcc():
    """Try to use GCC on OSX for OpenMP support."""
    # For macports and homebrew

    if 'darwin' in platform.platform().lower():
        gcc = extract_gcc_binaries()

        if gcc is not None:
            os.environ["CC"] = gcc
            os.environ["CXX"] = gcc

        else:
            global use_openmp
            use_openmp = False
            logging.warning('No GCC available. Install gcc from Homebrew '
                            'using brew install gcc.')