Fix and cleanup masm emitter.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15288 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Factorize emission of addressing modes for masm.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15289 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Cleanup.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15290 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02