FYI, I hacked together a new package definition, updating the emacs-next
one to build 29.1 from the release tarball, and after installing it,
everything seems to work, including native compilation.
I don't know enough about Guix to understand why using "guix install"
with the package transformation option caused the runtime problem with
gcc, but everything does seem to work with the updated definition.
So I guess this report can be closed.
OTOH, if anyone knows why the transformation option failed in that way,
it might be helpful to solve it if possible, so users could use the
option to install future releases without having to modify the package
definition. (AFAIK, I was able to do that for various Emacs 28 versions
without this problem, so I wonder if something's changed.)
See also: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=65000
