Fix missing header file in pxfheaders_test.c
Fix missing header file in pxfheaders_test.c

An elusive missing header file was detected when the Ubuntu job failed
in CI. Centos and Mac did not show any indication of a missing header
file and no side effects were detected. However, Ubuntu was returning an
int32 in makeDefElem instead of a 64-bit pointer.

Co-authored-by: Ashwin Agrawal <924bf3437ad315c1c74f9c41d83153600b05f548@pivotal.io>
Co-authored-by: Jesse Zhang <6775950e159d0bc2e58935ca2201ba88526dddf0@pivotal.io>
Co-authored-by: Francisco Guerrero <356157bf781222c6d0cb68cd14cecdf57676bd4b@pivotal.io>

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