Now, __constructor_order is boolean; 1 for forward-order systems,
0 for backward-order systems while parsing __LIST_APPEND().

Change it into a bool variable, and rename it for clarification.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>