Update stub for gc

stdlib/3/gc.pyi

@@ -1,10 +1,28 @@
 # Stubs for gc
 
-# NOTE: These are incomplete!
+from typing import Any, List, Tuple
 
-import typing
 
-def collect(generation: int = ...) -> int: ...
+DEBUG_COLLECTABLE = ... # type: int
+DEBUG_LEAK = ... # type: int
+DEBUG_SAVEALL = ... # type: int
+DEBUG_STATS = ... # type: int
+DEBUG_UNCOLLECTABLE = ... # type: int
+callbacks = ... # type: List[Any]
+garbage = ... # type: List[Any]
+
+def collect(generations: int = ...) -> int: ...
 def disable() -> None: ...
 def enable() -> None: ...
+def get_count() -> Tuple[int, int, int]: ...
+def get_debug() -> int: ...
+def get_objects() -> List[Any]: ...
+def get_referents(*objs: Any) -> List[Any]: ...
+def get_referrers(*objs: Any) -> List[Any]: ...
+def get_stats() -> List[Dict[str, Any]]: ...
+def get_threshold() -> Tuple[int, int, int]: ...
+def is_tracked(obj: Any) -> bool: ...
 def isenabled() -> bool: ...
+def set_debug(flags: int) -> None: ...
+def set_threshold(threshold0: int, threshold1: int = ...,
+                  threshold2: int = ...) -> None: ...