Provide MAP_FAILED if sys/mman.h doesn't.
Provide MAP_FAILED if sys/mman.h doesn't.

On old HPUX this has to be #defined to -1.  It might be that other values
are required on other dinosaur systems, but we'll worry about that when
and if we get reports.

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