Consider addrspaces in canLosslesslyBitCastTo()

Make this conservatively correct and report false for different
address spaces, which might require a nontrivial translation.

Based on the few uses of this, I don't think this currently
breaks anything.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216846 91177308-0d34-0410-b5e6-96231b3b80d8