rt_ssize_t can give negative error code, which follows the unix style correctly
* [rtdef] rename RT_WEAK attribute as rt_weak * [rtdef] rename RT_USED attribute as rt_used * [rtdef] rename RT_SECTION attribute as rt_section * [rtdef] rename ALIGN attribute as rt_align * [legacy] add RT_USED ALIGN RT_SECTION RT_WEAK as legacy support