MS ABI: Mangle alias templates used as template-template arguments

A templated using declaration may be used as a template-template
argument.

Unfortunately, the VS "14" chooses '?' as the sole marker for the
argument.  This is problematic because it presupposes the possibility of
using more than one template-aliases as arguments to the same template.

This fixes PR20047.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@214290 91177308-0d34-0410-b5e6-96231b3b80d8