[UBSan] Introduce type-based blacklisting.

Teach UBSan vptr checker to ignore technically invalud down-casts on
blacklisted types.

Based on http://reviews.llvm.org/D4407 by Byoungyoung Lee!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212770 91177308-0d34-0410-b5e6-96231b3b80d8