updated v5.6

[lrineau]

Updates to CGAL-5.6.

An upstream patch is required for PowerPC: CGAL/cgal#7635

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-webservices]

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

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

I do have some suggestions for making it better though...

For recipe:

• License is not an SPDX identifier (or a custom LicenseRef) nor an SPDX license expression.

Documentation on acceptable licenses can be found here.

[lrineau]

@conda-forge-admin, please rerender

[lrineau]

@tadeu: please delay the merge, because I would like to contribute CGAL-5.5.3 as well, before this one can be merged.