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

BUG: 851092
Change-Id: Ib298a492fee22dd82042af704fe8cdd34c3e100e
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/4998
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>