https://github.com/swiftlang/swift/blob/68c86413216b652978c8333155183bcea1ff5c97/lib/Frontend/ModuleInterfaceSupport.cpp#L337-L344 Builtinを使うには -parse-stdlib, -enable-builtin-module, -enable-experimental-feature BuiltinModule などの方法があるっぽい (edited)