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

stdlib/3/select.pyi

@@ -0,0 +1,27 @@
+# Stubs for select
+
+# NOTE: These are incomplete!
+
+from typing import Any, Tuple, List, Sequence
+
+class error(Exception): ...
+
+POLLIN = 0
+POLLPRI = 0
+POLLOUT = 0
+POLLERR = 0
+POLLHUP = 0
+POLLNVAL = 0
+
+class poll:
+    def __init__(self) -> None: ...
+    def register(self, fd: Any,
+                 eventmask: int = ...) -> None: ...
+    def modify(self, fd: Any, eventmask: int) -> None: ...
+    def unregister(self, fd: Any) -> None: ...
+    def poll(self, timeout: int = ...) -> List[Tuple[int, int]]: ...
+
+def select(rlist: Sequence, wlist: Sequence, xlist: Sequence,
+           timeout: float = ...) -> Tuple[List[int],
+                                           List[int],
+                                           List[int]]: ...