Generate a single call to divmod

Given the testcase in https://bugs.launchpad.net/gcc-linaro/+bug/637797 , we could end up generating a single call to divmod instead of separate calls to div and mod in a number of cases. There are 2 ways of fixing this one is to deal with it like sincos and the other cases or implement it with a fake call in the backend. I would rather we handled it like sincos optimization and dealt with it.