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

stdlib/2.7/signal.pyi

@@ -0,0 +1,62 @@
+from typing import Callable, Any, Tuple, Union
+from types import FrameType
+
+SIG_DFL = ...  # type: int
+SIG_IGN = ...  # type: int
+ITIMER_REAL = ...  # type: int
+ITIMER_VIRTUAL = ...  # type: int
+ITIMER_PROF = ...  # type: int
+
+SIGABRT = ...  # type: int
+SIGALRM = ...  # type: int
+SIGBUS = ...  # type: int
+SIGCHLD = ...  # type: int
+SIGCLD = ...  # type: int
+SIGCONT = ...  # type: int
+SIGFPE = ...  # type: int
+SIGHUP = ...  # type: int
+SIGILL = ...  # type: int
+SIGINT = ...  # type: int
+SIGIO = ...  # type: int
+SIGIOT = ...  # type: int
+SIGKILL = ...  # type: int
+SIGPIPE = ...  # type: int
+SIGPOLL = ...  # type: int
+SIGPROF = ...  # type: int
+SIGPWR = ...  # type: int
+SIGQUIT = ...  # type: int
+SIGRTMAX = ...  # type: int
+SIGRTMIN = ...  # type: int
+SIGSEGV = ...  # type: int
+SIGSTOP = ...  # type: int
+SIGSYS = ...  # type: int
+SIGTERM = ...  # type: int
+SIGTRAP = ...  # type: int
+SIGTSTP = ...  # type: int
+SIGTTIN = ...  # type: int
+SIGTTOU = ...  # type: int
+SIGURG = ...  # type: int
+SIGUSR1 = ...  # type: int
+SIGUSR2 = ...  # type: int
+SIGVTALRM = ...  # type: int
+SIGWINCH = ...  # type: int
+SIGXCPU = ...  # type: int
+SIGXFSZ = ...  # type: int
+NSIG = ...  # type: int
+
+class ItimerError(IOError): ...
+
+_HANDLER = Union[Callable[[int, FrameType], None], int, None]
+
+def alarm(time: int) -> int: ...
+def getsignal(signalnum: int) -> _HANDLER: ...
+def pause() -> None: ...
+def setitimer(which: int, seconds: float, interval: float = ...) -> Tuple[float, float]: ...
+def getitimer(which: int) -> Tuple[float, float]: ...
+def set_wakeup_fd(fd: int) -> int: ...
+def siginterrupt(signalnum: int, flag: bool) -> None:
+    raise RuntimeError()
+def signal(signalnum: int, handler: _HANDLER) -> _HANDLER:
+    raise RuntimeError()
+def default_int_handler(signum: int, frame: FrameType) -> None:
+    raise KeyboardInterrupt()