Do not keep the prehistoric gas bug on fsub/fsubrp/fdiv/fdivrp in the DSL.  Manage it purely in Intel_gas.

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_intel_emit@15249 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02