Fix pg_size_bytes() to be more portable.
Fix pg_size_bytes() to be more portable.

Commit 53874c5228fe16589a4d01b3e1fab3678e0fd8e3 broke various 32-bit
buildfarm machines because it incorrectly used an 'L' suffix for what
needed to be a 64-bit literal. Thanks to Michael Paquier for helping
to diagnose this.

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