The Nix project has been able to bootstrap an entire Linux distribution from scratch. However, doing that traditionally relies on binary seeds -- meaning the very first compiler in the chain is downloaded as a prebuilt binary rather than compiled from a fully verified source. This leaves a single foundational gap where users will have to trust trust an external black-box binary. Efforts toward reproducible builds and reducing this trust perimeter focus on removing binary seeds and tracing every compilation step back to a minimal, manually verifiable root.
Ken Thompson's Trusting Trust is an interesting conundrum... there are ways to minimize the need to trust however, if you can express everything in the same language or common runtime: