Give a more appropriate diagnostic when a template specialization or
instantiation appears in a non-enclosing namespace (the previous diagnostic
talked about the C++98 rule even in C++11 mode).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196642 91177308-0d34-0410-b5e6-96231b3b80d8