Use offsetof to calculate SVECHDRSIZE in accordance with the majority of HDRSIZE definitions
Use offsetof to calculate SVECHDRSIZE in accordance with the majority of HDRSIZE definitions

Removes a merge fixme

Reviewed-by: Heikki Linnakangas <9304c20251d03f4d84fc732cc8196e9ef6638e64@pivotal.io>

xinzweb/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,50wu/gpdb,xinzweb/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb