[asan] make sure asan erases old unused allocas after it created a new one. This became important after the recent move from ModulePass to FunctionPass because no cleanup is happening after asan pass any more. 

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@166267 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed