PR#6625: pass -linkpkg to files built with -output-obj.

(Peter Zotov)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15719 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
PR#6616: allow meaningful use of -use-runtime without -custom.

(Peter Zotov)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@15720 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02