An adventure of syncing rust and rustc_codegen_gcc

After two months, we were finally able to sync the GCC backend with the Rust compiler (something that usually takes a few hours).

I wrote a blog post about this sync in particular because it was quite the adventurer: https://blog.guillaume-gomez.fr/articles/2026-09-22+Syncing+Rust+GCC+backend+or+how+to+test+Murphy%27s+law