CI golf: try a better fix for tools install in Makefile.nt

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14541 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
minor Makefile.nt fix

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14542 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02