Removal of unexec support from glibc malloc

[Paul Eggert]

Florian Weimer wrote:
> this is a heads-up that glibc malloc will likely remove support code for
> the Emacs unexec mechanism during the coming year.

Thanks for that heads-up. Making the Emacs unexec mechanism more portable has 
been our to-do list for some time, and this will light more of a fire under it. 
We're already under a feature freeze for Emacs 25, though, so Emacs 25 will have 
to go out without the fix (which will be reasonably substantial, alas).

> This only affects the glibc API, so Emacs is unlikely to compile from
> source until you remove the undump mechanism.

Emacs should still build and run even if the glibc API is changed, as Emacs 
./configure probes for the glibc malloc-related API and falls back on its own 
malloc implementation otherwise. If some glitch prevents this from working with 
the new glibc API, I'd like to get this fixed before Emacs 25 comes out, so that 
Emacs 25 will build and run with newer glibc.

Can you explain the problem in more detail? What are the symptoms if you do the 
following with the next-generation glibc API?

git clone --branch emacs-25 git://git.savannah.gnu.org/emacs.git
cd emacs
./autogen.sh
./configure
make

Is there some way that Emacs developers (who are typically not glibc experts) 
can easily test with the next-generation glibc API?