Use OESeeror instead of os.error (#16720)

Patch by Serhiy Storchaka.
diff --git a/Tools/scripts/byext.py b/Tools/scripts/byext.py
index b79ff37..736a441 100755
--- a/Tools/scripts/byext.py
+++ b/Tools/scripts/byext.py
@@ -25,7 +25,7 @@
         self.addstats("<dir>", "dirs", 1)
         try:
             names = os.listdir(dir)
-        except os.error as err:
+        except OSError as err:
             sys.stderr.write("Can't list %s: %s\n" % (dir, err))
             self.addstats("<dir>", "unlistable", 1)
             return