swift-driver 側にも embedded WASI 関連の PR が出てますね． https://github.com/swiftlang/swift-driver/pull/1841

Fix incorrect link job options for embedded WASI by MaxDesiatov · P...

WebAssemblyToolchain didn't check for parsedOptions.isEmbeddedEnabled when forming swiftrt.o and static-executable-args.lnk options, and neither of these files exist when building with Embe...