Fix Windows-build failure: use my_snprintf() instead of snprintf().

tests/mysql_client_test.c

@@ -18524,14 +18524,14 @@ static void test_bug13001491()
 
   myheader("test_bug13001491");
 
-  snprintf(query, MAX_TEST_QUERY_LENGTH,
+  my_snprintf(query, MAX_TEST_QUERY_LENGTH,
            "GRANT ALL PRIVILEGES ON *.* TO mysqltest_u1@%s",
            opt_host ? opt_host : "'localhost'");
            
   rc= mysql_query(mysql, query);
   myquery(rc);
 
-  snprintf(query, MAX_TEST_QUERY_LENGTH,
+  my_snprintf(query, MAX_TEST_QUERY_LENGTH,
            "GRANT RELOAD ON *.* TO mysqltest_u1@%s",
            opt_host ? opt_host : "'localhost'");
            
@@ -18584,7 +18584,7 @@ static void test_bug13001491()
   mysql_close(c);
   c= NULL;
 
-  snprintf(query, MAX_TEST_QUERY_LENGTH,
+  my_snprintf(query, MAX_TEST_QUERY_LENGTH,
            "DROP USER mysqltest_u1@%s",
            opt_host ? opt_host : "'localhost'");