polly: Fix files that contain Python 3 SyntaxErrors

[cclauss]

These changes were originally in:

• OpenMP: Fix Python 3 SyntaxErrors #123940

They are moved here to enable a focused review by polly authors: @tobiasgrosser, @Meinersbur

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The polly/lib/External/isl/imath/tools/findthreshold.py changes were already made upstream:
https://github.com/creachadair/imath/blob/main/tools/findthreshold.py

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[Meinersbur]

Thanks for the PR. These are python2 source, and only syntax errors in Python3 (please fix the title accordingly).

threshold.py has been updated at creachadair/imath@03fc662. Changes in this repository will be overwritten the next time update-isl.py. It will pick the revision from https://repo.or.cz/isl.git/history/HEAD:/imath. To update that, contact the maintainer at [email protected]. The script is not used within Polly, hence I would rather not make changes here.

The other two need to complete update Python3. Did you actually execute these scripts to confirm they work with Python3.

[cclauss]

I modified the title as requested.

https://repo.or.cz/isl.git/history/HEAD:/imath returns a 500 error and poking around in
https://repo.or.cz/isl.git I am unable to find imath. I probably misunderstand this site.

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This pull request was not attempting to complete the port to Python 3. As recommended in the following locations, the pull request was only focused on stage-1 changes:

• https://portingguide.readthedocs.io/en/latest/process.html#port-the-code
• https://python-future.org/automatic_conversion.html#stage-1-safe-fixes

Proving that Python 2 tests still run successfully without Python 3 syntax errors is a gate before porting to Python 3. The upstream imath has already made stage 2 modifications by removing .iteritems() and .xrange() which changes Python 2 behavior.