[Flang] Port test_folding.sh to Python

[ijan1]

Summary

To enable Flang testing on Windows,
shells scripts have to be ported to Python.
The following changes have been made:
Ported test_folding.sh to Python;
Additional changes to the tests themselves
to use the new script.

LIBPGMATH support for testing
not available at this point.

[ijan1]

"folding21.f90" was added a few days ago and fails in all cases. It's not been set as "XFAIL" so I am unsure if that's something on my end.

[ijan1]

Hopefully fixes the few failing tests due to a regex issue.

[Meinersbur]

flang/test/Evaluate/test_folding.py

67

cf folding05.f90:
Consider specifying encoding="utf-8". Docs mention that the default-encoding is platform-dependent and it seems to be UTF-8 on Linux but cp1252 (Maybe dependent on localization) on Windows.

[ijan1]

Specified encoding to fix a failing test on Windows.

[ijan1]

@Meinersbur would it be fine to also disable these failings tests on Windows? I have filed a bug report on bugzilla[1] for D107956. I could include them there or file a new one.

[1] https://bugs.llvm.org/show_bug.cgi?id=51597

[ijan1]

Rebased to include newly added tests.

[ijan1]

Re-enabling some tests.

[ijan1]

Rebase to mollify buildbots.

[ijan1]

@Meinersbur is this one ready to be merged?

[Meinersbur]

LGTM

Please edit the commit messsage (remove Known test failures) before landing.