bug#61960: 30.0.50; Unexec build reliably crashes during loadup

[Eli Zaretskii]

> From: Andrea Corallo <akrl@sdf.org>
> Cc: 61960@debbugs.gnu.org, hi-angel@yandex.ru
> Date: Tue, 07 Mar 2023 14:59:24 +0000
> 
> >   if test "${with_native_compilation}" != "no"; then
> >       if test "${HAVE_PDUMPER}" = no; then
> >      AC_MSG_ERROR(['--with-native-compilation' requires 
> > '--with-dumping=pdumper'])
> >       fi
> 
> So IIUC we can compile emacs with both unexec and pdumper support, they
> are not mutually exclusive, and we can specify which one to use for the
> first dump with --with-dumping.
> 
> So yeah I think we have to prevent native compilation to be compiled
> with unexec support, even if it's not the way Emacs is dumped the first
> time.

OK, then a simple change to the above condition (and maybe a slight
change in the message wording as well) should achieve that, right?