Look through addrspacecast in GetPointerBaseWithConstantOffset

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212999 91177308-0d34-0410-b5e6-96231b3b80d8
Look through addrspacecast in IsConstantOffsetFromGlobal

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213000 91177308-0d34-0410-b5e6-96231b3b80d8