skip debugger test when dynlink is not available

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14490 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
commit mergeinfo to keep svn happy

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14491 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02