new upstream, spec cleanups
    
    - Upstream removed the exit() calls https://github.com/jgaeddert/liquid-dsp/issues/134
    - invoke autoreconf at build time, as upstream doesn't package what we need
    - Add BR: fftw-devel
    - Remove BR: gcovr and --enable-coverage. It was keeping the exit call in the library,
      and we aren't looking at the coverage results anyhow.