MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)

The bug is not very important per se, but it was helpful to move
Item_func_strcmp out of Item_bool_func2 (to Item_int_func),
for the purposes of "MDEV-4912 Add a plugin to field types (column types)".

mysql-test/r/func_test.result

@@ -320,3 +320,20 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 Warnings:
 Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where (not((`test`.`t1`.`a` + 0)))
 drop table t1;
+#
+# Start of 10.0 tests
+#
+#
+# MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)
+#
+SELECT NOT NOT strcmp('a','b');
+NOT NOT strcmp('a','b')
+1
+EXPLAIN EXTENDED SELECT NOT NOT strcmp('a','b');
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
+Warnings:
+Note	1003	select (strcmp('a','b') <> 0) AS `NOT NOT strcmp('a','b')`
+#
+# End of 10.0 tests
+#

mysql-test/r/null.result

@@ -382,3 +382,15 @@ CREATE TABLE t2 (d DATE) ENGINE=MyISAM;
 SELECT  * FROM t1,t2 WHERE  1 IS NOT NULL AND t1.b IS NULL;
 a	b	c	d
 DROP TABLE t1,t2;
+#
+# Start of 10.0 tests
+#
+#
+# MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3) 
+#
+SELECT NOT NOT NULLIF(2,3);
+NOT NOT NULLIF(2,3)
+1
+#
+# End of 10.0 tests
+#

mysql-test/t/func_test.test

@@ -180,3 +180,17 @@ select * from t1 where not (a+0);
 explain extended select * from t1 where not (a+0);
 
 drop table t1;
+
+--echo #
+--echo # Start of 10.0 tests
+--echo #
+
+--echo #
+--echo # MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3)
+--echo #
+SELECT NOT NOT strcmp('a','b');
+EXPLAIN EXTENDED SELECT NOT NOT strcmp('a','b');
+
+--echo #
+--echo # End of 10.0 tests
+--echo #

mysql-test/t/null.test

@@ -295,3 +295,16 @@ CREATE TABLE t2 (d DATE) ENGINE=MyISAM;
 SELECT  * FROM t1,t2 WHERE  1 IS NOT NULL AND t1.b IS NULL;
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # Start of 10.0 tests
+--echo #
+
+--echo #
+--echo # MDEV-7001 Bad result for NOT NOT STRCMP('a','b') and NOT NOT NULLIF(2,3) 
+--echo #
+SELECT NOT NOT NULLIF(2,3);
+
+--echo #
+--echo # End of 10.0 tests
+--echo #