Flutter.framework is distributed as a fat binary (arm64, x86_64) to allow running on both devices and simulator. This causes App Store validation to fail due to the including of x86_64 code in the final binary.

We should add an additional build phase that strips framework code to the target architecture with lipo, for example to xcodebackend.sh. e.g., http://ikennd.ac/blog/2015/02/stripping-unwanted-architectures-from-dynamic-libraries-in-xcode/