Build: treat `SwiftDriver` as a private link dependency
Build: treat `SwiftDriver` as a private link dependency

This module is marked as `@_implementationOnly`.  The users of `Build`
should not have to link against `SwiftDriver`.

apple/swift-package-manager,abertelrud/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager,apple/swift-package-manager,abertelrud/swift-package-manager