Clean-up warnings for non native builds

Clean-up warnings for non native builds

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