Merge emit.mlp and emit_nt.mlp using an abstract x86 assembler

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_x86_asm@14397 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Reverting previous erroneous commit and going back to revision r14396

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_x86_asm@14398 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
Fix small issue with new amd64/emit.mlp

git-svn-id: http://caml.inria.fr/svn/ocaml/branches/abstract_x86_asm@14399 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02