The problem statement is a multi-table UPDATE statement, with an updated
table that is joined to a join of two tables, enclosed in a derived table.
In 5.6, the derived table was materialized into a temporary table, and the
join was optimized properly.
In 5.7, the derived table is still materialized, but it is not optimized,
it performs as if a STRAIGHT_JOIN option has been added to the query block.

A multi-table UPDATE statement does not allow semi-joined subqueries,
thus the option SELECT_STRAIGHT_JOIN is added when optimizing subqueries.
However, this option also affects join optimization, so in effect this
means adding the STRAIGHT_JOIN option to the derived table subquery.
Thus, the join is performed in a non-optimal way.

The solution is to set the flag semijoin_disallowed for all query blocks
of the derived table to trigger no semi-join transformation for this case.
The SELECT_STRAIGHT_JOIN option is kept as-is, thus explicitly
specifying the STRAIGHT_JOIN in either the parent or the child query block
will still prevent semi-join transformation.

Reviewed by: Guilhem Bichot <guilhem.bichot@oracle.com>