Switch macOS SDK to 11.0 for Python 3.8 (for testing)

[bkpoon]

This is a draft pull request to build Boost.Python 1.74 packages for testing builds and runtime environments.

This is to match the switch for Python 3.8 from
conda-forge/python-feedstock@da95584

The related issue is conda-forge/cctbx-base-feedstock#22

Basically, some Boost.Python conversions behave differently with python-3.8.10_h0e5c897_0_cpython vs python-3.8.10_h3a889e0_1_cpython for osx-64 (the rest of the environment remains the same). Other versions of Python for osx-64 are not affected. The osx-arm64 builds for Python 3.8.10 do not show the issue. The other platforms, linux-64 and win-64, are not affected.

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I was trying to look for recipes to lint for you, but it appears we have a merge conflict.
Please try to merge or rebase with the base branch to resolve this conflict.

Please ping the 'conda-forge/core' team (using the @ notation in a comment) if you believe this is a bug.

[bkpoon]

I'm not sure why the Azure Pipelines builds did not start, but I'm building it here. https://dev.azure.com/cctbx-release/feedstock-builds/_build?definitionId=3&_a=summary

And it looks like I have to update the download location.

[bkpoon]

Looks like my issue persists even after rebuilding with the new SDK. It's odd since Python 3.9.4 is also built with the latest macOS SDK and links to CoreFoundation, but does not exhibit my issue on osx-64 with the boost 1.74 package for Python 3.9. I'll close this and do some more debugging.

[jakirkham]

Could you please file an issue with a simple reproducer? Would be good to get some clarity on what isn't working

[bkpoon]

Sure, I just made #117. Let me know if any more information is needed.

[jakirkham]

Thanks! 😄