Add Apple Silicon architecture for macOS

[Shakarang]

Checklist

• All tests are passed.
• Added tests.
• Documented the code using Xcode markup.
• Searched existing pull requests for ensure not duplicated.

Description

Apple will release the the architecture Apple Silicon. To make it work with DifferenceKit, we need to add arm64 to the valid architectures of macOS builds.

Related Issue

#118

Motivation and Context

It allows us to use DifferenceKit on Apple Silicon Mac.

Impact on Existing Code

Nothing.

[Kaspik]

Valid Archs is not valid settings anymore in XCode 12, does it still work?

[Shakarang]

Valid Archs is not valid settings anymore in XCode 12, does it still work?

Yes, we are still using this in Xcode 12.3

[taoshotaro]

I think you need to fix the xcconfig. https://github.com/ra1028/DifferenceKit/blob/master/XCConfigs/DifferenceKit.xcconfig

[ra1028]

Fixed #124