Builds of gpyfft for kFreeBSD (admittedly not a release architecture)
have been failing:

  Traceback (most recent call last):
    File "setup.py", line 39, in <module>
      include_dirs= CLFFT_INCL_DIRS + CL_INCL_DIRS,
  NameError: name 'CLFFT_INCL_DIRS' is not defined

I expect builds for the Hurd (not a release architecture either) would
fail in the same fashion if python-opencl were to become available
there.  (From what I gather, it's waiting for an OpenCL ICD.)

In general, I see that setup.py features hardcoded path settings that
are specific to the upstream developer's systems and has no provision
for operating systems other than Linux, Windows, and macOS.  Until
upstream removes these settings, I would encourage explicitly
resetting them on all platforms.

Could you please take a look?

Thanks!