introduce __floor__ and __ceil__ for int in Python 3 (#3306)

stdlib/2/__builtin__.pyi

@@ -185,6 +185,8 @@ class int:
     def __invert__(self) -> int: ...
     def __trunc__(self) -> int: ...
     if sys.version_info >= (3,):
+        def __ceil__(self) -> int: ...
+        def __floor__(self) -> int: ...
         def __round__(self, ndigits: Optional[int] = ...) -> int: ...
     def __getnewargs__(self) -> Tuple[int]: ...