llvm-vtabledump: A vtable dumper

This tool's job is to dump the vtables inside object files.  It is
currently limited to MS ABI vf- and vb-tables but it will eventually
support Itanium-style v-tables as well.

Differential Revision: http://reviews.llvm.org/D4584

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213903 91177308-0d34-0410-b5e6-96231b3b80d8