WIP: gnuradio: new package

FIXME: at least uhd_fft fail at runtime:

1st run:
    File "/nix/store/lclnhhxbifp2qzjgr00gc8gsvr3lk4zq-gnuradio-3.6.4.1/lib/python2.7/site-packages/gnuradio/gr/hier_block2.py", line 54, in __getattr__
      return getattr(self._hb, name)
  AttributeError: 'gr_hier_block2_sptr' object has no attribute 'set_callback'

2nd run:
  RuntimeError: AssertionError: libusb_submit_transfer(_lut) == 0
    in virtual void libusb_zero_copy_mrb::release()
    at
  /tmp/nix-build-uhd-3.5.2.drv-0/UHD-Mirror-release_003_005_002/host/lib/transport/libusb1_zero_copy.cpp:101

How old is the 3.6.4.1 release? Build from git instead?
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Add GNU Radio, the free & open-source software development toolkit that
provides signal processing blocks to implement sofware radios.