Only check for 'test/wheeldata' when it's actually used

It's possible to build Python with option `--with-wheel-pkg-dir`
pointing to a custom wheel directory. Don't include the directory in the test
set if the wheels are used from a different location.

Lib/test/test_tools/test_makefile.py

@@ -67,6 +67,9 @@ def test_makefile_test_folders(self):
                 )
                 used.append(relpath)
 
+        if sysconfig.get_config_var('WHEEL_PKG_DIR'):
+            test_dirs.remove('test/wheeldata')
+
         # Check that there are no extra entries:
         unique_test_dirs = set(test_dirs)
         self.assertSetEqual(unique_test_dirs, set(used))