Remove volatile qualifiers from lwlock.c.
Remove volatile qualifiers from lwlock.c.

Now that spinlocks (hopefully!) act as compiler barriers, as of commit
0709b7ee72e4bc71ad07b7120acd117265ab51d0, this should be safe.  This
serves as a demonstration of the new coding style, and may be optimized
better on some machines as well.

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