MariaRocks: fix compilation on kvm-rpm-centos7-amd64

Define __STDC_FORMAT_MACROS before using PRIu64.
RocksDB does this in many files

storage/rocksdb/rdb_sst_info.cc

@@ -14,6 +14,9 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
+/* For PRIu64 use below: */
+#define __STDC_FORMAT_MACROS
+
 #include <my_config.h>
 
 /* This C++ file's header file */