Issue a diagnostic if an implicitly-defined move assignment operator would move
the same virtual base class multiple times (and the move assignment is used,
and the move assignment for the virtual base is not trivial).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193977 91177308-0d34-0410-b5e6-96231b3b80d8