Revert "Revert r211402 (and r211408,r211410), "CodeGen: Refactor dynamic_cast and typeid" It crashes msvc codegen in clang/test/SemaCXX/undefined-internal.cpp."

This reverts commit r211467 which reverted r211408,r211410, it caused
crashes in test/SemaCXX/undefined-internal.cpp for i686-win32 targets.