Reproduce the issue:
---
# go to Python source tree
mkdir build
cd build
../configure
make
./python -m test test_sys
---

Output:

======================================================================
FAIL: test_stdlib_dir (test.test_sys.SysModuleTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/python/main/Lib/test/test_sys.py", line 1005, in test_stdlib_dir
    self.assertEqual(actual, expected)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: '/home/vstinner/python/main/build/../Lib' != '/home/vstinner/python/main/Lib'
- /home/vstinner/python/main/build/../Lib
?                            ---------
+ /home/vstinner/python/main/Lib


Attached PR fix the issue.