MDEV-16708: Unsupported commands for prepared statements

Fixed failures of the tests main.compound, main.union

mysql-test/main/compound.result

@@ -101,7 +101,7 @@ t1
 t2
 t3
 t4
-set @a=0;
+set @a=0|
 repeat
 set @a = @a + 1;
 until @a > 5
@@ -154,7 +154,7 @@ master-bin.000001	#	Query	#	#	use `test`; insert t1 values( NAME_CONST('a',4)+3)
 master-bin.000001	#	Query	#	#	COMMIT
 drop function fn|
 drop table t1|
-set @@sql_mode="STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION";
+set @@sql_mode="STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"|
 begin not atomic select @@sql_mode; end|
 @@sql_mode
 STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION

mysql-test/main/compound.test

@@ -94,7 +94,7 @@ end loop|
 show tables|
 
 # REPEAT
-set @a=0;
+set @a=0|
 repeat
   set @a = @a + 1;
 until @a > 5
@@ -146,7 +146,7 @@ drop table t1|
 # MDEV-6609 SQL inside an anonymous block is executed with wrong SQL_MODE
 #
 
-set @@sql_mode="STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION";
+set @@sql_mode="STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"|
 begin not atomic select @@sql_mode; end|
 create table t1 (a int)|
 select a from t1 having a > 1|

mysql-test/main/union.test

@@ -93,6 +93,7 @@ select 1 as a,(select a union select a);
 SELECT @a:=1 UNION SELECT @a:=@a+1;
 --error 1054
 (SELECT 1) UNION (SELECT 2) ORDER BY (SELECT a);
+--sorted_result
 (SELECT 1,3) UNION (SELECT 2,1) ORDER BY (SELECT 2);
 
 #