PR#6590: Improve Windows (MSVC and mingw) build

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15461 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
sync configure with the bdf.h objinfo change

(Patch by Christopher Zimmermann)

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15463 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
minor configure changes

git-svn-id: http://caml.inria.fr/svn/ocaml/version/4.02@15464 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02