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
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