bpo-37064: Skip test_tools.test_pathfix if installed (GH-15705) (GH-16389)

If Python is installed, skip test_tools.test_pathfix test because
Tools/scripts/pathfix.py script is not installed.

(cherry picked from commit 3f43cef)

Author: vstinner

Lib/test/test_tools/test_pathfix.py

@@ -3,7 +3,11 @@
 import sys
 import unittest
 from test import support
-from test.test_tools import import_tool, scriptsdir
+from test.test_tools import import_tool, scriptsdir, skip_if_missing
+
+
+# need Tools/script/ directory: skip if run on Python installed on the system
+skip_if_missing()
 
 
 class TestPathfixFunctional(unittest.TestCase):