If we attempt to add a constructor template specialization that looks

like a copy constructor to the overload set, just ignore it. This
ensures that we don't try to use such a constructor as a copy
constructor *without* triggering diagnostics at the point of
declaration.

Note that we *do* diagnose such copy constructors when explicitly
written by the user (e.g., as an explicit specialization).

llvm-svn: 88733