cmake HAVE_UNIX_DNS_SRV examples

GreatSQL/GreatSQL libmysql/CMakeLists.txt :243 

UNSET(HAVE_UNIX_DNS_SRV)

percona/percona-server libmysql/CMakeLists.txt :254 

UNSET(HAVE_UNIX_DNS_SRV)

facebook/mysql-5.6 libmysql/CMakeLists.txt :263 

UNSET(HAVE_UNIX_DNS_SRV)

logicalclocks/rondb libmysql/CMakeLists.txt :264 

UNSET(HAVE_UNIX_DNS_SRV)

polardb/polardbx-engine libmysql/CMakeLists.txt :243 

UNSET(HAVE_UNIX_DNS_SRV)

mysql/mysql-server libmysql/CMakeLists.txt :258 

UNSET(HAVE_UNIX_DNS_SRV)

percona/percona-xtrabackup libmysql/CMakeLists.txt :258 

UNSET(HAVE_UNIX_DNS_SRV)

percona/percona-xtradb-cluster libmysql/CMakeLists.txt :255 

UNSET(HAVE_UNIX_DNS_SRV)