gh-139823: Check if zlib is available in ensurepip

[StanFromIreland]

• Issue: make install fails in ensurepip if zlib extension is missing #139823

[pfmoore]

To be honest, I'm not sure I see the value of this. Then again, I didn't see the logic of withdrawing the "make zlib required" PEP... Particularly given that ensurepip (and pip) are not used or functional on WASI (the key platform withlout zlib), it feels like making ensurepip more friendly for zlib-less builds of Python is pretty pointless.

But equally, it's not a big burden to add this test, so I'm not going to object (beyond the request for a clarifying comment in the test code that I included below).

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[StanFromIreland]

I didn't see the logic of withdrawing the "make zlib required" PEP...

I think we can leave PEP-775 for a different discussion.

Particularly given that ensurepip (and pip) are not used or functional on WASI (the key platform withlout zlib), it feels like making ensurepip more friendly for zlib-less builds of Python is pretty pointless.

I think this error message is not for WASI, but for people who unintentionally built Python without zlib, or omitted it but wish to use ensurepip and are surprised by the long error message they receive (an example would be the linked issue).

This proposal also received support on the linked issue (3 thumbs up).

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I will improve the comment in the test, apologies for the confusion it caused.

[StanFromIreland]

I have made the requested changes; please review again

[bedevere-app]

Thanks for making the requested changes!

@pfmoore: please review the changes made to this pull request.