[minor] Makefile.nt typo

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14545 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
[minor] make tools/Makefile.shared msvc-friendly

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14547 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02