Expand supported gcc versions.

[bdice]

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.

Resolves #33.

[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.

[jakirkham]

Thanks Bradley! 🙏

Added more context in comment ( #33 (comment) )

Agree with Isuru that we don't need the constraints here

Though think the logic here can be simplified (please see linked comment for more detail)

[bdice]

I checked the built artifacts and the changes look correct now. @jakirkham gave me the go-ahead to merge after verifying this.

[jakirkham]

Thanks Bradley and Isuru! 🙏