resgroup: fix compile warnings with --disable-cassert.
resgroup: fix compile warnings with --disable-cassert.

Some functions are only used in `assert()`, put these functions in
`#ifdef USE_ASSERT_CHECKING` to prevent compilation warnings.

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