Move contents of builtins/* to stdlib/*. This simplifies finding stubs.

stdlib/2.7/xxsubtype.pyi

@@ -0,0 +1,17 @@
+"""Stub file for the 'xxsubtype' module."""
+
+from typing import Any
+
+def bench(obj: Any, name: str, n:int = ...) -> float: ...
+
+class spamdict(dict):
+    state = ...  # type: int
+    def getstate(self) -> int: ...
+    def setstate(self, a: int) -> None: ...
+
+class spamlist(list):
+    state = ...  # type: int
+    def getstate(self) -> int: ...
+    def setstate(self, a: int) -> None: ...
+    def classmeth(self, *args, **kwargs) -> tuple: ...
+    def staticmeth(self, *args, **kwargs) -> tuple: ...