MDEV-12657 A few tests fail in build-bot on Windows after changing...

MDEV-12657 A few tests fail in build-bot on Windows after changing Field::field_name and Item::name to LEX_CSTRING

sql/item.cc

@@ -8762,7 +8762,7 @@ bool Item_default_value::fix_fields(THD *thd, Item **items)
   real_arg= arg->real_item();
   if (real_arg->type() != FIELD_ITEM)
   {
-    my_error(ER_NO_DEFAULT_FOR_FIELD, MYF(0), arg->name);
+    my_error(ER_NO_DEFAULT_FOR_FIELD, MYF(0), arg->name.str);
     goto error;
   }
 

sql/partition_info.cc

@@ -1922,7 +1922,7 @@ void partition_info::report_part_expr_error(bool use_subpart_expr)
         !(type == HASH_PARTITION && list_of_fields))
     {
       my_error(ER_FIELD_TYPE_NOT_ALLOWED_AS_PARTITION_FIELD, MYF(0),
-               item_field->name);
+               item_field->name.str);
       DBUG_VOID_RETURN;
     }
   }

sql/sql_class.cc

@@ -3134,7 +3134,7 @@ int select_export::send_data(List<Item> &items)
                             ER_TRUNCATED_WRONG_VALUE_FOR_FIELD,
                             ER_THD(thd, ER_TRUNCATED_WRONG_VALUE_FOR_FIELD),
                             "string", printable_buff,
-                            item->name, static_cast<long>(row_count));
+                            item->name.str, static_cast<long>(row_count));
       }
       else if (copier.source_end_pos() < res->ptr() + res->length())
       { 

sql/sql_view.cc

@@ -156,7 +156,7 @@ bool check_duplicate_names(THD *thd, List<Item> &item_list, bool gen_unique_view
   DBUG_RETURN(FALSE);
 
 err:
-  my_error(ER_DUP_FIELDNAME, MYF(0), item->name);
+  my_error(ER_DUP_FIELDNAME, MYF(0), item->name.str);
   DBUG_RETURN(TRUE);
 }