Add valgrind suppression for pg_atomic_init_u64.
Add valgrind suppression for pg_atomic_init_u64.

pg_atomic_init_u64 (indirectly) uses compare/exchange to guarantee
atomic writes on platforms where compare/exchange is available, but
64bit writes aren't atomic (yes, those exist). That leads to a
harmless read of the initial value of variable.

greenplum-db/gpdb,techdragon/Postgres-XL,adam8157/gpdb,ovr/postgres-xl,techdragon/Postgres-XL,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,ovr/postgres-xl,jmcatamney/gpdb,ovr/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,yazun/postgres-xl,ovr/postgres-xl,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb,oberstet/postgres-xl,techdragon/Postgres-XL,xinzweb/gpdb,lisakowen/gpdb,yazun/postgres-xl,adam8157/gpdb,jmcatamney/gpdb,yazun/postgres-xl,oberstet/postgres-xl,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,pavanvd/postgres-xl,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,oberstet/postgres-xl,ashwinstar/gpdb,pavanvd/postgres-xl,jmcatamney/gpdb,oberstet/postgres-xl,adam8157/gpdb,lisakowen/gpdb,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,greenplum-db/gpdb,zeroae/postgres-xl,Postgres-XL/Postgres-XL,jmcatamney/gpdb,zeroae/postgres-xl,greenplum-db/gpdb,xinzweb/gpdb,yazun/postgres-xl,ashwinstar/gpdb,ovr/postgres-xl,Postgres-XL/Postgres-XL,ashwinstar/gpdb,lisakowen/gpdb,greenplum-db/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,xinzweb/gpdb,lisakowen/gpdb,oberstet/postgres-xl,zeroae/postgres-xl,ashwinstar/gpdb,50wu/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,zeroae/postgres-xl,greenplum-db/gpdb,jmcatamney/gpdb,Postgres-XL/Postgres-XL,greenplum-db/gpdb,adam8157/gpdb,adam8157/gpdb,yazun/postgres-xl,50wu/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,ashwinstar/gpdb,ashwinstar/gpdb