Retrobootstrapping Rust for some reason

Summary

Elsewhere I've been asked about the task of replaying the bootstrap process for rust. I figured it would be fairly straightforward, if slow. But as we got into it, there were just enough tricky / non-obvious bits in the process that it's worth making some notes here for posterity.contextRust started its life as a compiler written in ocaml, called rustboot. This compiler did not use LLVM, it just emitted 32-bit i386 machine code in 3 object file formats (Linux PE, macOS Mach-O, and Windows PE).We then wrote a second compiler in Rust called rustc that did use LLVM as its backend (and which, yes, is the genesis of today's rustc) and ran rustboot on rustc to produce a so-called "stage0 rustc". Then stage0 rustc was fed the sources of rustc again, producing a stage1 rustc. Successfully executing this stage0 -> stage1 step (rather than just crashing mid-compilation) is what we're going to call "bootstrapping". There's also a third step: running stage1 rustc on rustc's sources again to get a stage2 rustc and checking that it is bit-identical to the stage1 rustc. Successfully doing that we're going to call "fixpoint".Shortly after we reached the fixpoint we discarded rustboot. We stored stage1 rustc binaries as snapshots on a shared download server and all subsequent rust builds were based on downloading and running that. Any time there was an incompatible language change made, we'd add support and re-snapshot the resulting stage1, gradually growing a long list of snapshots marking the progress of rust over time.time travel and bit rotEach snapshot can typically only compile rust code in the rust repository written between its birth and the next snapshot. This makes replay of replaying the entire history awkward. We're not going to do that here. This post is just about replaying the initial bootstrap and fixpoint, which happened back in April 2011, 14 years ago.Unfortunately all the tools involved -- from the host OS and system libraries involved to compilers and compiler-c...