Use Literal in a few more places (#3176)

stdlib/3/_winapi.pyi

@@ -1,5 +1,11 @@
+import sys
 from typing import Any, Union, Tuple, Optional, overload, Dict, NoReturn, Sequence
 
+if sys.version_info >= (3, 8):
+    from typing import Literal
+else:
+    from typing_extensions import Literal
+
 CREATE_NEW_CONSOLE: int
 CREATE_NEW_PROCESS_GROUP: int
 DUPLICATE_CLOSE_SOURCE: int
@@ -46,11 +52,12 @@ WAIT_TIMEOUT: int
 
 def CloseHandle(handle: int) -> None: ...
 
-# TODO: once literal types are supported, overload with Literal[True/False]
 @overload
-def ConnectNamedPipe(handle: int, overlapped: Union[int, bool]) -> Any: ...
+def ConnectNamedPipe(handle: int, overlapped: Literal[True]) -> Overlapped: ...
 @overload
-def ConnectNamedPipe(handle: int) -> None: ...
+def ConnectNamedPipe(handle: int, overlapped: Literal[False] = ...) -> None: ...
+@overload
+def ConnectNamedPipe(handle: int, overlapped: bool) -> Any: ...
 
 def CreateFile(file_name: str, desired_access: int, share_mode: int, security_attributes: int, creation_disposition: int, flags_and_attributes: int, template_file: int) -> int: ...
 def CreateJunction(src_path: str, dest_path: str) -> None: ...

stdlib/3/ast.pyi

@@ -1,12 +1,9 @@
-# Python 3.5 ast
-
 import sys
 # Rename typing to _typing, as not to conflict with typing imported
 # from _ast below when loaded in an unorthodox way by the Dropbox
 # internal Bazel integration.
 import typing as _typing
 from typing import overload, Any, Iterator, Optional, Union, TypeVar
-from typing_extensions import Literal
 
 # The same unorthodox Bazel integration causes issues with sys, which
 # is imported in both modules. unfortunately we can't just rename sys,
@@ -14,6 +11,11 @@ from typing_extensions import Literal
 # sys.
 from _ast import *  # type: ignore
 
+if sys.version_info >= (3, 8):
+    from typing import Literal
+else:
+    from typing_extensions import Literal
+
 class NodeVisitor():
     def visit(self, node: AST) -> Any: ...
     def generic_visit(self, node: AST) -> Any: ...

stdlib/3/gettext.pyi

@@ -1,7 +1,10 @@
-# Stubs for gettext (Python 3.4)
-
+import sys
 from typing import overload, Any, Container, IO, Iterable, Optional, Type, TypeVar
-from typing_extensions import Literal
+
+if sys.version_info >= (3, 8):
+    from typing import Literal
+else:
+    from typing_extensions import Literal
 
 class NullTranslations:
     def __init__(self, fp: IO[str] = ...) -> None: ...

stdlib/3/subprocess.pyi

@@ -7,9 +7,13 @@ from typing import (
     Generic, TypeVar, AnyStr,
     overload,
 )
-from typing_extensions import Literal
 from types import TracebackType
 
+if sys.version_info >= (3, 8):
+    from typing import Literal
+else:
+    from typing_extensions import Literal
+
 # We prefer to annotate inputs to methods (eg subprocess.check_call) with these
 # union types.
 # For outputs we use laborious literal based overloads to try to determine