[Bug c++/57764] class static constexpr variables cannot be references

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57764

--- Comment #2 from Paolo Carlini <paolo.carlini at oracle dot com> ---
This is fixed in 4.9.0 and mainline. I'm adding the testcase and closing the
bug.