routingtable not defined the first time in parallel mode

```rst
Indices and tables
==================

* :ref:`routingtable`
* :ref:`genindex`
* :ref:`modindex`
* :ref:`search`
```

On a clean build produces:

```
.../docs/index.rst:28: WARNING: undefined label: routingtable
```

Specifically with the command `sphinx-build -j auto -n $SRC/docs $SRC/docs/_build/html`.