This patch introduces the -fwhole-program-vtables flag, which enables the
whole-program vtable optimization feature (D16795) in Clang.

Differential Revision: http://reviews.llvm.org/D16821

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@261767 91177308-0d34-0410-b5e6-96231b3b80d8