IR: Add a helper to check for LinkOnceODRLinkage

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212078 91177308-0d34-0410-b5e6-96231b3b80d8
GlobalOpt: Handle non-zero offsets for aliases

An alias with an aliasee of a non-zero GEP is not trivially replacable
with it's aliasee.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212079 91177308-0d34-0410-b5e6-96231b3b80d8