porting: OSX build fixes

 - xml build
 - do not redefine AT_SYMLINK_FOLLOW

Change-Id: I516b3713904a6bad946a30f76fe4821f2ac61fd3
BUG: 1130307
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/8970
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Kaleb KEITHLEY <kkeithle@redhat.com>