fix regression (extraneous moves) caused by previous Cconst_blockheader patch

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14648 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
part 2: fix regression (extraneous moves) caused by previous Cconst_blockheader patch

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14649 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02