fix builds on 9.5 and 9.6

Author: funbringer

src/utils.c

@@ -26,6 +26,7 @@
 #include "parser/parse_oper.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
+#include "utils/datetime.h"
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
 #include "utils/syscache.h"