Don't modify mutable default arguments...

After 1a3e8db28d49, Windows XP could not os.stat at all due to raising
immediately when GetFinalPathNameByHandle wasn't available (pre-Vista).
The proper behavior in that situation is to just not attempt a traversal
rather than outright rejecting.

This change additionally handles a failed malloc by setting the error code
and returning false.

Patch by Hirokazu Yamamoto.

Use of DeviceIoControl to obtain the symlink path via the reparse tag was
removed. The code now uses GetFinalPathNameByHandle in the case of a
symbolic link and works properly given the added test which creates a symbolic
link and calls os.stat on it from multiple locations.

Victor Stinner also noticed an issue with os.lstat following the os.stat
code path when being passed bytes. The posix_lstat function was adjusted to
properly hook up win32_lstat instead of the previous STAT macro (win32_stat).

Spawn a new process instead of using fork(). Patch written by Charles-François
Natali.

This allows findsource() to work in doctests.

A patch from Dirkjan Ochtman.

methods.

Original patch by Erik Bray.

Original patch by Erik Bray.

Original patch by Erik Bray as part of #11595, changed by me to improve
readability.