This uses the same class metadata currently used for virtual call and
cast checks.

The new flag is -fsanitize=cfi-nvcall. For consistency, the -fsanitize=cfi-vptr
flag has been renamed -fsanitize=cfi-vcall.

Differential Revision: http://reviews.llvm.org/D8756

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@233874 91177308-0d34-0410-b5e6-96231b3b80d8