Selecting the address from a very long chain of GEPs can blow the stack.

The recursive nature of the address selection code can cause the stack to
explode if there is a long chain of GEPs. Convert the recursive bit into a
iterative method to avoid this.

<rdar://problem/12445434>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191252 91177308-0d34-0410-b5e6-96231b3b80d8