C++, cpp:var item rejected in in cpp:function

ping @jakobandersen

I've been using cpp:var items inside cpp:function items to help document behaviours etc., and this is now being rejected. For instance:

.. cpp:function:: template<typename It> void foo(It start, It stop)

    .. cpp:var:: auto const length = std::distance(start, stop)

        The notional distance between the two iterators.

    :complexity: :math:`\Theta(length)`

This used to be accepted, with references in cpp:expr or cpp:texpr linking to the appropriate places and such. This now results in something like:

WARNING: C++ declarations inside functions are not supported. Parent function is foo()

This looks to be related to the #5191 fix.