[Bug c++/71504] [C++11] constexpr fails with multidimensional arrays

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71504

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Created attachment 46968
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46968&action=edit
partial fix

This fixes handling of references to the first object, but not later ones, so
several of the testcases in this PR still fail.  Putting this aside for now.