Fix ABI size

Author: ZeroIntensity

Include/internal/pycore_atexit.h

@@ -44,6 +44,7 @@ typedef struct {
 
 struct atexit_state {
     atexit_callback *ll_callbacks;
+    atexit_callback *last_ll_callback;
 
     // XXX The rest of the state could be moved to the atexit module state
     // and a low-level callback added for it during module exec.