Fix UBSan bootstrap: don't bind reference to nullptr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224751 91177308-0d34-0410-b5e6-96231b3b80d8
Fix UBSan bootstrap: replace shift of negative value with multiplication.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224752 91177308-0d34-0410-b5e6-96231b3b80d8