[ARM64,C++11] Clean up the ARM64 LOH collection pass.

Range'ify a bunch of loops, mainly. As a result, we have a variety
of objects via reference rather than by pointer, so propogate that
through the various helper functions where it makes sense.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206337 91177308-0d34-0410-b5e6-96231b3b80d8