I5ec4ab44c4e88aaf18c0d7b73355d27050beeda7 almost fixed this bug, but we
also have to make it possible to access builtin variables as arrays.
This will only make sense for a few variables (e.g. added_lines and
removed_lines), but I don't think we should validate it when checking
syntax.
Bug: T198531
Change-Id: I417e1b8d4802bbfccd091ce5c7617659cfd1e4ea