[2.6] multirhstest tries to put a simd type into an ostream

Job #72996 failed for 9af998aa:

In file included from /builds/core/dune-istl/dune/istl/test/multirhstest.cc:31:
/builds/core/dune-istl/dune/istl/solvers.hh:627:22: error: invalid operands to binary expression ('basic_ostream<char, std::char_traits<char> >' and 'Dune::InverseOperator<Dune::BlockVector<Dune::FieldVector<Vc_1::SimdArray<double, 2, Vc_1::Vector<double, Vc_1::VectorAbi::Scalar>, 1>, 1>, Dune::AlignedAllocator<Dune::FieldVector<Vc_1::SimdArray<double, 2, Vc_1::Vector<double, Vc_1::VectorAbi::Scalar>, 1>, 1>, -1> >, Dune::BlockVector<Dune::FieldVector<Vc_1::SimdArray<double, 2, Vc_1::Vector<double, Vc_1::VectorAbi::Scalar>, 1>, 1>, Dune::AlignedAllocator<Dune::FieldVector<Vc_1::SimdArray<double, 2, Vc_1::Vector<double, Vc_1::VectorAbi::Scalar>, 1>, 1>, -1> > >::field_type' (aka 'Vc_1::SimdArray<double, 2, Vc_1::Vector<double, Vc_1::VectorAbi::Scalar>, 1>'))
                     << rho << " <= EPSILON " << max_value(EPSILON)
                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/duneci/modules/dune-common/dune/common/exceptions.hh:217:58: note: expanded from macro 'DUNE_THROW'
                              th__out << THROWSPEC(E) << m; th__ex.message(th__out.str()); throw th__ex; \
                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~^