Split stdlib into Python 2 and 3 versions (#5442)

All new files in stdlib/@python2 are straight copies of the
corresponding files in stdlib.

stdlib/@python2/syslog.pyi

@@ -0,0 +1,43 @@
+from typing import overload
+
+LOG_ALERT: int
+LOG_AUTH: int
+LOG_CONS: int
+LOG_CRIT: int
+LOG_CRON: int
+LOG_DAEMON: int
+LOG_DEBUG: int
+LOG_EMERG: int
+LOG_ERR: int
+LOG_INFO: int
+LOG_KERN: int
+LOG_LOCAL0: int
+LOG_LOCAL1: int
+LOG_LOCAL2: int
+LOG_LOCAL3: int
+LOG_LOCAL4: int
+LOG_LOCAL5: int
+LOG_LOCAL6: int
+LOG_LOCAL7: int
+LOG_LPR: int
+LOG_MAIL: int
+LOG_NDELAY: int
+LOG_NEWS: int
+LOG_NOTICE: int
+LOG_NOWAIT: int
+LOG_PERROR: int
+LOG_PID: int
+LOG_SYSLOG: int
+LOG_USER: int
+LOG_UUCP: int
+LOG_WARNING: int
+
+def LOG_MASK(a: int) -> int: ...
+def LOG_UPTO(a: int) -> int: ...
+def closelog() -> None: ...
+def openlog(ident: str = ..., logoption: int = ..., facility: int = ...) -> None: ...
+def setlogmask(x: int) -> int: ...
+@overload
+def syslog(priority: int, message: str) -> None: ...
+@overload
+def syslog(message: str) -> None: ...