PR#6588 part 2: for ARMv4 and ARMv5, make sure architectural constraints
  on the "smull" instruction are respected.  (Patch by Mark Shinwell.)


git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15498 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02