test_tensordot fails to compile

[papadop]

Current git version tests fail to compile when building test_tensordot.cpp.o. The message (repeated several times) is: /usr/include/xtensor/xiterator.hpp:324:86: error: invalid use of incomplete type ‘struct xt::detail::LAYOUT_FORBIDEN_FOR_XITERATOR<(xt::layout_type)0>’ using checking_type = typename detail::LAYOUT_FORBIDEN_FOR_XITERATOR<L>::type; ^ /usr/include/xtensor/xiterator.hpp:271:16: note: declaration of ‘struct xt::detail::LAYOUT_FORBIDEN_FOR_XITERATOR<(xt::layout_type)0>’ struct LAYOUT_FORBIDEN_FOR_XITERATOR; ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is with gcc version 8.3.1 20190223 (Red Hat 8.3.1-2) (GCC)