Since this is to try and avoid crashes on shutdown, it will either
be available and work, or linking will fail, which will be detected
by configure, and thus we will not use it.
* configure.ac: Add HAVE_FREE_HOOK when __free_hook is available.
Also fix detection of __after_morecore_hook.
* src/emacs.c (voodoo_free_hook): Ignore the warning about
deprecated variable.
* src/emacs.c (Fkill_emacs): Ditto.
Signed-off-by: Nelson Ferreira <nelson.ferreira@ieee.org>