Let llvm.objectsize be conservative with null pointers

This adds a parameter to @llvm.objectsize that makes it return
conservative values if it's given null.

This fixes PR23277.

Differential Revision: https://reviews.llvm.org/D28494


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298430 91177308-0d34-0410-b5e6-96231b3b80d8
16 files changed