Add dummy PQsslAttributes function for non-SSL builds.
Add dummy PQsslAttributes function for non-SSL builds.

All the other new SSL information functions had dummy versions in
be-secure.c, but I missed PQsslAttributes(). Oops. Surprisingly, the linker
did not complain about the missing function on most platforms represented in
the buildfarm, even though it is exported, except for a few Windows systems.

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