swift/utils/update_checkout/update-checkout-config.jsonにYamsのチェックアウト情報が載る様になってると気づいて調べたら、SwiftPMで--use-integrated-swift-driverオプションとか使える様になってたのね。 https://github.com/apple/swift-package-manager/pull/2736

[Build] Add support for building with the integrated Swift driver b...

Add bootstrap and build support for building the new Swift driver and importing it (as a library) into SwiftPM. Then introduce the new SwiftPM flag --use-integrated-swift-driver to enable use of th...