[Bug libstdc++/91558] [C++11] should not be constexpr until C++14

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91558

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Yichen Yan from comment #3)
> (In reply to Jonathan Wakely from comment #1)
> > (In reply to Yichen Yan from comment #0)
> > > Detail: 
> > > Constexpr for <complex> is in C++14 if I don't misunderstand. But a lot of
> > > testcases under libstdc++-v3/testsuite/26_numerics/complex/ (e.g. 
> > > dr844.cc)
> > 
> > Are you sure? That test doesn't seem to care about constexpr.
> 
> Yes, check_ret_type require its template argument and argument to be
> constexpr.

No it doesn't:

  template<typename R, typename T>
    typename __gnu_cxx::__enable_if<std::__are_same<R, T>::__value,
                                    bool>::__type
    check_ret_type(T)
    { return true; }