Fix aarch64 build

[isuruf]

Checklist

• [ ] Used a 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 code>@<space/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 wanted to let you know that I linted all conda-recipes in your PR (recipe) and found some lint.

Here's what I've got...

For recipe:

• The home item is expected in the about section.
• The license item is expected in the about section.
• The summary item is expected in the about section.
• The outputs section contained an unexpected subsection name. target is not a valid subsection name.
• The outputs section contained an unexpected subsection name. target is not a valid subsection name.
• The outputs section contained an unexpected subsection name. target is not a valid subsection name.
• The outputs section contained an unexpected subsection name. target is not a valid subsection name.

[isuruf]

Because there's no need. That mutex is there for avoiding pkgs/free and cf201901 packages mixing with pkgs/main and gcc7 packages from mixing.

[isuruf]

@conda-forge-admin, rerender