bug#33174: 27.0.50; Dump fails on GNU/Linux ppc64le

[Thomas Fitzsimmons <fitzsim@fitzsim.org>]

Hi Paul,

On ppc64le Debian GNU/Linux 9, I'm seeing a bootstrap failure on the
master and emacs-26 branches that I didn't see the last time I built
Emacs:

[...]
Dumping under the name emacs
**************************************************
Warning: Your system has a gap between BSS and the
heap (424960392 bytes).  This usually means that exec-shield
or something similar is in effect.  The dump may
fail because of this.  See the section about
exec-shield in etc/PROBLEMS for more information.
**************************************************
22496304 of 33554432 static heap bytes used
Makefile:749: recipe for target 'bootstrap-emacs' failed
make[1]: *** [bootstrap-emacs] Segmentation fault
make[1]: Leaving directory '/home/fitzsim/sources/emacs/src'
Makefile:421: recipe for target 'src' failed
make: *** [src] Error 2

I bisected the failure to:

commit 65889a6d127fcbbbdc1e74d26036e91bd24d1405
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Sun Jul 8 09:04:02 2018 -0700

    Fix bootstrap infloop in GNU/Linux alpha
    
    * src/emacs.c (main): Do not re-exec if EMACS_HEAP_EXEC
    is already set (Bug#32083).

If I revert that commit's patch, the build succeeds.

Thomas