Fix out-of-tree build problems with loaddefs.el

Fix out-of-tree build problems with loaddefs.el

* lisp/Makefile.in ($(lisp)/loaddefs.el): Use the new function.

* lisp/emacs-lisp/loaddefs-gen.el (loaddefs-generate): Pass in
whether to inhibit a partial build (to make the code more general).
(loaddefs-generate--emacs-batch): Add a new function specially for
the Emacs build that has the special rules needed.  (This also
fixes out-of-tree builds.)
loaddefs-generate-batch can be used in general for packages etc.
(loaddefs-generate-batch): Remove the special code for Emacs builds.