'ReusingBase' was a terrible name. It might actually refer to the most
derived class, which is not a base. 'BaseWithVPtr' was also bad, since
again, it could refer to the most derived class. It was actually the
first base to introduce the vptr, so now it is 'IntroducingObject'.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@276120 91177308-0d34-0410-b5e6-96231b3b80d8