It seems like it's an ever-elusive topic, but I have been working on being able to cross compile Swift 5.10.1 (stdlibs and corelibs only) to armv7 using a Debian 12 sysroot and run it on my Raspberry Pi. Since I hate not sharing such knowledge, I've created I guide on my blog here:
My hope is that anyone else who is interested in targeting an armv7 board can use these instructions as a starting point. I am working on pull requesting my cross compilation buildbot profile back to swiftlang/swift, but who knows if that'll get accepted. Either way, it's just another step towards the dream of eventually having an official build of Swift for armv7!