bpo-45506: Normalize _PyPathConfig.stdlib_dir when calculated.

[ericsnowcurrently]

The recently added PyConfig.stdlib_dir was being set with ".." entries. When __file__ was added for from modules this caused a problem on out-of-tree builds. This PR fixes that by normalizing "stdlib_dir" when it is calculated in getpath.c.

https://bugs.python.org/issue45506

[gpshead]

./python -m test.regrtest test_embed -v still fails in an out of tree build for me with this change. As does test_gdb. Both appear to be having trouble importing encodings? Others such as test_importlib no longer fail.

[bedevere-bot]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[warsaw]

I ran the full test suite:

8 tests failed:
    test_compileall test_embed test_import test_importlib test_inspect
    test_pyclbr test_socket test_unittest

[warsaw]

Even with this PR, test_embed and test_unittest still fail.

[ericsnowcurrently]

Hmm, I don't get failures in test_unittest. At this point, I've fixed the problem with test_embed and only need to deal with failures in subprocess due to that first commit.

[ericsnowcurrently]

With that latest commit I got all the tests to pass in an out-of-tree build.

[gpshead]

I believe this one is good. test_embed still fails for me using this branch but I think there was another PR you already merged that addressed that.

[bedevere-bot]

@ericsnowcurrently: Please replace # with GH- in the commit message next time. Thanks!