bug#74382: `compile-first` Make rule is no longer using `load-prefer-newer`

[Eli Zaretskii <eliz@gnu.org>]

> From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> Cc: gerd.moellmann@gmail.com, acm@muc.de, 74382@debbugs.gnu.org
> Date: Sun, 17 Nov 2024 18:43:17 +0300
> 
> On Sun, 2024-11-17 at 17:37 +0200, Eli Zaretskii wrote:
> > > Cc: Alan Mackenzie <acm@muc.de>, 74382@debbugs.gnu.org
> > > From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> > > Date: Sun, 17 Nov 2024 18:21:36 +0300
> > > 
> > > On Sun, 2024-11-17 at 08:25 +0100, Gerd Möllmann wrote:
> > > > Konstantin Kharlamov <Hi-Angel@yandex.ru> writes:
> > > > 
> > > > > Sure, I just reproduced it after removing all `.elc` files in
> > > > > the
> > > > > repo,
> > > > > here how:
> > > > > 
> > > > > 1. `git checkout f2f13fa630b` (a commit from April)
> > > > > 2. `make -j$(nproc)` to compile. Note: you don't need to wait
> > > > > for
> > > > > build
> > > > > to finish, I just waited for all files under `lisp/emacs-lisp`
> > > > > directory to finish compilation, and then ^C'ed it.
> > > > > 3. `git checkout 29098a291f5` (a November commit).
> > > > > 4. `make -j$(nproc)`
> > > > 
> > > > This would always work if lisp/Makefile would rm the .elc files
> > > > from
> > > > COMPILE_FIRST, right? I suspect this isn't done to speed up the
> > > > build
> > > > in
> > > > the usual case, and because it's a bit difficult to automatically
> > > > determine if it has to done or not.
> > > > 
> > > > Does a "make clean" after the checkout in (3) make it work?
> > > 
> > > I don't think so, because `make clean` for some reason doesn't
> > > remove
> > > `.elc` artifacts.
> > 
> > And it shouldn't, because *.elc files are part of a release tarball.
> 
> But if someone decided to build from a release tarball, sure they can
> produce .elc files as well, can't they?

No, Emacs release tarballs come with *.elc files, and users shouldn't
recompile them.  For starters, it makes the build significantly
longer, besides being unnecessary.

Recompiling *.elc files is only needed if the corresponding *.el files
are modified, something that doesn't normally happen when you build a
release tarball.