bug#71729: Emacs 29.4 emergency bugfix release

[Adam Porter]

Hello,

Today an emergency bugfix release was made of Emacs v29.4.  It fixes an 
important security vulnerability.

FWIW, I had hoped that I could install it by running:

  guix install --with-version=emacs=29.4 emacs

But that fails the validate-comp-integrity phase, showing that all of 
its tests fail, with every function being loaded in byte-compiled form 
instead of native-compiled.

And despite my best efforts at comparing the emacs.git tags for 29.3 and 
29.4 to look for any relevant changes, and digging through the relevant 
source code, and scanning through the build logs, I can't find a cause 
for this problem.

Is this failure expected?  If so, is it something unique to the Emacs 
packaging, and could it be fixed?  (Before Emacs 28 was released, I was 
able to use a similar "--with-commit" option to build and install what 
was then the emacs-next package to get native-compilation support, 
keeping it updated with Emacs's master branch at the time.  It would be 
helpful if that could still be used by users rather than having to wait 
for an update to the package definition, especially in a case like this.)

Thanks for your work on Emacs in Guix.

--Adam