Compile tk on mac without the aqua option

[smithsp]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• 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.

This PR is a work in progress. I assume that the conda-forge tk admins don't want to always disable aqua on mac, and I am trying to take what @dsentinel started in https://github.com/dsentinel/tk-feedstock/commits/mac_noaqua to see if that compiles, and then work to implement a noaqua variant that makes the desired changes.

[conda-forge-linter]

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.

[smithsp]

@conda-forge/tk
I believe that this is ready for review. One problem that is outstanding is that I only want a noaqua variant to be built on osx, for which I added a selector in the conda_build_config.yaml file, but then the linux rendering of the meta.yaml fails, because apparently my variant tk_aqua has no value. That seems like a bug in conda to not allow a single value variant or in jinja to not allow the setting of the tk_aqua variable with the line {% set tk_aqua = tk_aqua or 'aqua' %}.

[smithsp]

@conda-forge-admin, please rerender

[smithsp]

@conda-forge/tk Ping

[smithsp]

@conda-forge-admin, please rerender

[dsentinel]

Thanks for this. This timing is great, as our workarounds are getting more cumbersome.