[Bug c++/72777] broken error message with reference in constexpr arguments in c++11 mode

[bloerwald at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72777

--- Comment #1 from bloerwald at googlemail dot com ---
Note: compiles fine in c++11 mode of clang 3.8, so not sure if it actually is
forbidden by the standard.