Make build cancelled/failed when it can not be fully done from cache.

Description

Hello,

let's imagine:

I have an exotic case where I have to do some very compute-intensive compilation for non-x86 architecture. To increase the speed, I spin up an instance with the needed architecture in the cloud (e.g. AWS EC2) and spawn a buildkit builder in it and do my build in this remote builder.

For the next builds (until I make some changes and invalidate the cache) I won't need to spin up a remote builder because
everything will be cached, so it would be great to be able to perform the next set of actions:

1. Try to do a build that will fail/cancel if it can not be fully done from the cache.
2. a. If there is a cache miss, then the build fails and I spin up a remote builder and do another build in it.
   b. If there is no cache-miss, then everything is cool and I don't have to do anything else.

For now, if you run build locally and cache-miss has happened. There's no way to stop that build.

PS: Sorry, it seems that this request has to be in the buildkit project, not here. I would be glad to keep it open anyway in case I missed something and solution already exists.

The issue names no files or tests. Start by tracing the local build path and how BuildKit reports cache misses or cancellation; done means a build can stop when any work cannot be completed entirely from cache and can distinguish that result from a successful cache-only build.