Fix broken linux build

* Generic linux does not have property_get_int32. Instead,
  osi_property_get_int32() is created to handle OS_GENERIC cases
* Some linux header have sigevent.sigev_notify_attributes typed as
  (pthread_attr_t *) whereas others typed it as (void *), as any pointer
  can be implicitly casted to (void *), the current casting to (void *)
  is unncessary and will break build on systems using (pthread_attr_t *)

Test: make, unit test, no user visible effect
Change-Id: I24b33da453dc9d40656168a3bcd900d9c99219ce