Fixing a couple of asan-identified bugs
* use of an invalid "Use" iterator after the element was removed
* use of StringRef to Function name after the Function was erased
This reapplies r371567, which was reverted in r371580.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@371700 91177308-0d34-0410-b5e6-96231b3b80d8