ZOOKEEPER-4654: Fix C client test compilation error in Util.cc.

Author: Chris Nauroth <cnauroth@apache.org>

Reviewers: Enrico Olivelli <eolivelli@apache.org>, Mate Szalay-Beko <symat@apache.org>

Closes #1967 from cnauroth/ZOOKEEPER-4654

zookeeper-client/zookeeper-client-c/tests/Util.cc

@@ -16,6 +16,8 @@
  * limitations under the License.
  */
 
+#include <time.h>
+
 #include "Util.h"
 #include "string.h"