The parser is allocating Item_field for references by name in ORDER BY
 expressions. Such expressions however may point not only to Item_field 
 in the select list (or to a table column) but also to an arbitrary Item. 
 This causes Item_field::fix_fields to throw an error about missing 
 column.
 The fix substitutes Item_field for the reference with an Item_ref when 
 not pointing to Item_field.


mysql-test/r/order_by.result:
  Bug #22457: Column alias in ORDER BY works, but not if in an expression
   - test case
mysql-test/t/order_by.test:
  Bug #22457: Column alias in ORDER BY works, but not if in an expression
   - test case
sql/item.cc:
  Bug #22457: Column alias in ORDER BY works, but not if in an expression
   - transform the Item_field made by the parser into Item_ref if it 
     doesn't point to Item_field and it is in allowed context