configure.ac: enable-debug change breaks _hardened_build

See RHBZ 955283, and http://fedoraproject.org/wiki/Packaging:Guidelines#PIE

The previous change for BZ 851092 in
commit 058a736f9e36238c284ca80e7ed5f62434655019
breaks the ability to enable _hardened_build in release-3.4 and master

wrt test/bugs/bug-884455.t; passes on master/HEAD, passes on my dev box,
passed once with prove -rfvc in run-tests.sh.

BUG: 851092
Change-Id: Ic2afc53bcdf11ede4a543b87aa7c7a3a41ed6f1d
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/4997
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>