bpo-31802: Fix importing native path module before importing os. (#4017)

Lib/posixpath.py

@@ -10,6 +10,18 @@ Some of this can actually be useful on non-Posix systems too, e.g.
 for manipulation of the pathname component of URLs.
 """
 
+# Strings representing various path-related bits and pieces.
+# These are primarily for export; internally, they are hardcoded.
+# Should be set before imports for resolving cyclic dependency.
+curdir = '.'
+pardir = '..'
+extsep = '.'
+sep = '/'
+pathsep = ':'
+defpath = ':/bin:/usr/bin'
+altsep = None
+devnull = '/dev/null'
+
 import os
 import sys
 import stat
@@ -25,16 +37,6 @@ __all__ = ["normcase","isabs","join","splitdrive","split","splitext",
            "devnull","realpath","supports_unicode_filenames","relpath",
            "commonpath"]
 
-# Strings representing various path-related bits and pieces.
-# These are primarily for export; internally, they are hardcoded.
-curdir = '.'
-pardir = '..'
-extsep = '.'
-sep = '/'
-pathsep = ':'
-defpath = ':/bin:/usr/bin'
-altsep = None
-devnull = '/dev/null'
 
 def _get_sep(path):
     if isinstance(path, bytes):