When parsing statements like (SELECT .. FROM ..) ORDER BY <expr>,
there is a step LEX::add_tail_to_query_expression_body_ext_parens()
which calls LEX::wrap_unit_into_derived(). After that the statement
looks like SELECT * FROM (SELECT .. FROM ..), and parser's
Lex_order_limit_lock structure (ORDER BY <expr>) is assigned to
the new SELECT. But what is missing here is that Items in
Lex_order_limit_lock are left with their original name resolution
contexts, and fix_fields() later resolves the names incorrectly.

For example, when processing
  (SELECT * FROM t1 JOIN t2 ON a=b) ORDER BY a
Item_field 'a' in the ORDER BY clause is left with the name resolution
context of the derived table (first_name_resolution_table='t1'), so
it is resolved to 't1.a', which is incorrect.
After LEX::wrap_unit_into_derived() the statement looks like
  SELECT * FROM (SELECT * FROM t1 JOIN t2 ON a=b) AS '__2' ORDER BY a,
and the name resolution context for Item_field 'a' in the ORDER BY
must be set to the wrapping SELECT's one.

This commit fixes the issue by changing context for Items in
Lex_order_limit_lock after LEX::wrap_unit_into_derived().