add support for alpine-based images

[zg]

Alpine Linux is a security-oriented, lightweight Linux distribution based on musl libc and busybox. A container requires no more than 8 MB and a minimal installation to disk requires around 130 MB of storage. The slimness of Alpine Linux makes it an attractive base image for use in production environments, namely Kubernetes, where it incurs a smaller startup latency and reduces image size in a Docker registry.

[stevapple]

You’ll need to port Swift to musl before you can get an Alpine image. Of course, we welcome such effort very much.

[Gustl22]

See: swiftlang/swift#47209

[finagolfin]

@al45tair, any plans for this, building on your Musl work?

[al45tair]

I think it's probably worth returning to this question after WWDC. Alpine wasn't the focus of what I was up to with Musl, and making it work is in principle possible, but in practice I think we'd need to make significant upstream changes to Musl itself (which would then need to filter down into Alpine). I don't want to rule it out, because I know people will be interested in Alpine support, and the work I've been doing will make it easier, but it's still not trivial.