emacs: fix the detection of native compilation for Emacs 29

In Emacs 29, feature comp does not load early enough. We use
native-compile instead. This is also what Emacs uses[1].

[1]: https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/startup.el?id=3685387e609753293c4518be75e77c659c3b2d8d#n586

Lin Jian 2d324ed8 6505082e

Changed files
+1 -1
pkgs
applications
editors
+1 -1
pkgs/applications/editors/emacs/site-start.el
···
(mapconcat 'identity new-env-list ":"))))))
;;; Set up native-comp load path.
-
(when (featurep 'comp)
;; Append native-comp subdirectories from `NIX_PROFILES'.
(setq native-comp-eln-load-path
(append (mapcar (lambda (profile-dir)
···
(mapconcat 'identity new-env-list ":"))))))
;;; Set up native-comp load path.
+
(when (featurep 'native-compile)
;; Append native-comp subdirectories from `NIX_PROFILES'.
(setq native-comp-eln-load-path
(append (mapcar (lambda (profile-dir)