[Transforms][ASan] Move findAllocaForValue() to Utils/Local.cpp. NFC

Summary:
Factor out findAllocaForValue() from ASan so that we can use it in
MSan to handle lifetime intrinsics.

Reviewers: eugenis, pcc

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60615

llvm-svn: 358380