Bug#31081 server crash in regexp function

Problem: The "regex" library written by Henry Spencer
does not support tricky character sets like UCS2.
Fix: convert tricky character sets to UTF8 before calling
regex functions.

mysql-test/include/ctype_regex.inc

@@ -0,0 +1,42 @@
+#
+# To test a desired collation, set session.collation_connection to
+# this collation before including this file
+#
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+
+#
+# Create a table with two varchar(64) null-able column,
+# using current values of
+# @@character_set_connection and  @@collation_connection.
+#
+
+create table t1 as
+select repeat(' ', 64) as s1, repeat(' ',64) as s2
+union
+select null, null;
+show create table t1;
+delete from t1;
+
+insert into t1 values('aaa','aaa');
+insert into t1 values('aaa|qqq','qqq');
+insert into t1 values('gheis','^[^a-dXYZ]+$');
+insert into t1 values('aab','^aa?b');
+insert into t1 values('Baaan','^Ba*n');
+insert into t1 values('aaa','qqq|aaa');
+insert into t1 values('qqq','qqq|aaa');
+
+insert into t1 values('bbb','qqq|aaa');
+insert into t1 values('bbb','qqq');
+insert into t1 values('aaa','aba');
+
+insert into t1 values(null,'abc');
+insert into t1 values('def',null);
+insert into t1 values(null,null);
+insert into t1 values('ghi','ghi[');
+
+select HIGH_PRIORITY s1 regexp s2 from t1;
+
+drop table t1;