This implements the review suggestion to simplify the AArch64 backend. If we
later discover that we *really* need the extra complexity of the
ConstantIslands pass for performance reasons it can be resurrected.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175258 91177308-0d34-0410-b5e6-96231b3b80d8