[Bug c++/123577] C++17: Unhelpful constexpr error message when array size exceeds 16 bytes

[ajcozzol at us dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123577

--- Comment #1 from Anthony Cozzolino <ajcozzol at us dot ibm.com> ---
Note: I'm not sure if leaving ret uninitialized is actually a constexpr
violation to begin with, but since that is being enforced in C++17 mode, it
would be nice to have a proper error message.