[arm] Optimize integer division and modulus by constant.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14259 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
[arm] r12 is destroyed for constants that are not a power of 2.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14260 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02