Clean-up warnings for non native builds (this time for real)

Clean-up warnings for non native builds (this time for real)

* lisp/emacs-lisp/comp.el (comp-native-version-dir)
(comp-subr-arities-h, native-comp-eln-load-path)
(native-comp-enable-subr-trampolines): Remove warning.
(comp--compile-ctxt-to-file, comp--init-ctxt, comp--release-ctxt)
(comp-el-to-eln-filename)
(comp-el-to-eln-rel-filename, native-elisp-load): Declare.
* lisp/emacs-lisp/comp-run.el (comp--no-native-compile)
(comp-deferred-pending-h, comp-installed-trampolines-h)
(native-comp-enable-subr-trampolines): Remove warning.
(comp--install-trampoline, comp-el-to-eln-filename)
(native-elisp-load): Declare.
* lisp/emacs-lisp/comp-common.el: Update.