Function lean_sys::lean_set_non_heap_header

pub unsafe fn lean_set_non_heap_header(
    o: *mut lean_object,
    sz: usize,
    tag: c_uint,
    other: c_uint
)

Remark: we don’t need a reference counter for objects that are not stored in the heap. Thus, we use the area to store the object size for small objects.