Add missing build dependency of hoc_module. (#1277)

* Add missing dependency of `hoc_module` on `rxd_cython_generated`
* This declares that src/nrnpython/setup.py depends on generated .cpp
  files such as share/lib/python/neuron/rxd/geometry3d/graphicsPrimitives.cpp
  and fixes build errors.

src/nrnpython/CMakeLists.txt

@@ -260,6 +260,9 @@ if(NRN_ENABLE_MODULE_INSTALL)
   endforeach(pyexe)
 
   add_dependencies(hoc_module nrniv_lib ${nrnpython_lib_list})
+  if(NRN_ENABLE_RX3D)
+    add_dependencies(hoc_module rxd_cython_generated)
+  endif()
 
   #~~~
   # neuron module (possibly with multiple extension versions) was built