linking with GNU Radio FFT library

[address@hidden]

gr-acars is working very well with GNU Radio 3.8, all good. Now I'd like
to add two improvements: being able to run multiple processing blocks in
parallel (on multiple channels, which libfftw seems hardly able to do due to
the non-threadable plan creation) and getting rid of the external FFTW 
dependency
since GNU Radio provides its own FFT wrapper around libfftw3.

So I converted all fftw calls to internal GNU Radio calls, the software 
compiles fine
 and now I am stuck with executing since any call to 
 fft::fft_complex* plan_2400 = new fft::fft_complex(N, true);
leads to
 AttributeError: module 'acars' has no attribute 'acars'
when executing in GNU Radio Companion, which I attribute to a missing library 
dependency.

I have tried to follow 
https://wiki.gnuradio.org/index.php/OutOfTreeModulesConfig 
but the documentation seems outdated since it refers the 3.7.0 requirements.
I tried following 
https://raw.githubusercontent.com/gnuradio/gnuradio/master/cmake/Modules/GrComponent.cmake
as used in https://github.com/gnuradio/gnuradio/tree/master/gr-qtgui but that
too seems a dead end.

1/ is the CMakeLists configuration

include(GrComponent)
GR_REGISTER_COMPONENT("gr-acars" ENABLE_GNURADIO_RUNTIME ENABLE_GR_FFT)
find_package(Gnuradio "3.8" REQUIRED)

the correct way of linking with the FFT library ?
2/ is there a basic example of a simple OOT block linking on such a library 
somewhere ?

Thanks, JM

--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 26 rue de l'Epitaphe,
25000 Besancon, France