CodeGen: Start using inrange annotations on vtable getelementptr.

This annotation allows the optimizer to split vtable groups, as permitted by
a change to the Itanium ABI [1] that prevents compilers from adjusting virtual
table pointers between virtual tables.

[1] https://github.com/MentorEmbedded/cxx-abi/pull/7

Differential Revision: https://reviews.llvm.org/D24431