参考https://github.com/flutter/flutter/issues/33909
Xcode 10 SDK seems not to include i386 architecture.
Can't build Flutter engine with Xcode 10 because it removed i386 support
Xcode 10 removed 32-bit stubs for linking against the macOS SDK.
temporary solution for iOS is to remove armv7 and armv7s from Valid architectures in Build Settings section. It drops support for iPhone 5, iPhone 5C, iPad 4 and older devices