We have a static inline in hwloc/helper.h to replace the old
get_system_obj() into the new get_root_obj(). But there are other API
changes in 1.0 which have no similar compat wrapper. For instance
replacing HWLOC_OBJ_PU instead of HWLOC_OBJ_PROC probably broke every
hwloc user on earth. So I tend to think that we should just drop the
get_system_obj() and make it clear that people have to fix everything,
not everything except foo and bar.