Fix some warnings

[adamkaplan]

Description

Fix a few warnings, linter and Xcode 12

Motivation and Context

Build improvements

How Has This Been Tested?

n/a

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

License

I confirm that this contribution is made under an MIT license and that I have the authority necessary to make this contribution on behalf of its copyright owner.

[dbgrandi]

Oh... We need to add some CI to this.