Add msvcrt.locking() and associated constants (#3607)

stdlib/2and3/msvcrt.pyi

@@ -0,0 +1,14 @@
+# Stubs for msvcrt
+
+# NOTE: These are incomplete!
+
+LK_LOCK: int
+LK_NBLCK: int
+LK_NBRLCK: int
+LK_RLCK: int
+LK_UNLCK: int
+
+def locking(fd: int, mode: int, nbytes: int) -> None: ...
+
+def get_osfhandle(file: int) -> int: ...
+def open_osfhandle(handle: int, flags: int) -> int: ...