Recommitting Craig Topper's patch now that r296476 has been recommitted.

When checking if chain node is foldable, make sure the intermediate nodes have a single use across all results not just the result that was used to reach the chain node.

This recovers a test case that was severely broken by r296476, my making sure we don't create ADD/ADC that loads and stores when there is also a flag dependency.

llvm-svn: 297698