MS ABI: Add a vftable test for pure virtual methods

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@218965 91177308-0d34-0410-b5e6-96231b3b80d8
MS ABI: Move test from virtual-inheritance to single-inheritance

The test didn't actually use virtual inheritance.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@218966 91177308-0d34-0410-b5e6-96231b3b80d8