Bug#963659: pybind11: FTBFS with Sphinx 3.1: File "/usr/lib/python3/dist-packages/sphinx/domains/c.py", line 3093, in object_type / raise NotImplementedError())

[Drew Parsons]

Still failing with breathe 4.20.0-1 (and sphinx 3.2.1-1, pybind11 
2.5.0-4).