GCC 7 generates (when compiling in C++11/14 mode) warnings such as:

    mangled name for ‘pybind11::class_<type_, options>&
    pybind11::class_<type_, options>::def(const char*, Func&&, const Extra&
    ...) [with Func = int (test_exc_sp::C::*)(int) noexcept; Extra = {};
    type_ = test_exc_sp::C; options = {}]’ will change in C++17 because the
    exception specification is part of a function type [-Wnoexcept-type]

There's nothing we can actually do in the code to avoid this, so just
disable the warning.