[Bug c++/60771] static in-class constexpr const reference initialization

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60771

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed by the commit which fixed c++/50473 (r217672). I'm adding the
testcase and closing the bug.