[Bug c++/124214] Templated class with static constexpr method compiles without warning about non C++11 compliant body

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124214

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
That's intentional, in the current C++ standard it's only an error when you try
to use that function during constant evaluation.

For a function template marked 'constexpr', not all specializations will be
usable in constant expressions. If a given specialization is not usable in a
constant expression, the 'constexpr' is just ignored.