[ms-cxxabi] Give the MS inheritance attributes a base class

Required making a handful of changes to the table generator.  Also adds
an unspecified inheritance attribute.  This opens the path for us to
apply these attributes to C++ records implicitly.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178054 91177308-0d34-0410-b5e6-96231b3b80d8