Revert "[ubsan] Reduce null checking of C++ object pointers (PR27581)"

Revert "[ubsan] Reduce null checking of C++ object pointers (PR27581)"

This reverts commit r295391. It breaks this bot:

http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/1898

I need to not rely on labels in the IR test.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@295396 91177308-0d34-0410-b5e6-96231b3b80d8