If building a native toolchain, GCC by default does a 3-stage bootstrap build (https://gcc.gnu.org/install/configure.html). In addition to making sure that GCC is able to reproduce itself bit-by-bit, this also means that stages 2+ are built with -Werror (turning most warning into error diagnostics; see --enable-werror, possibly enabled by default). This helps to catch a good number of bugs, because it enforces that GCC compiles without compiler diagnostics; it's a requirement for upstream patch submission (https://gcc.gnu.org/contribute.html#testing).

The GCC/Rust instructions explicitly specify --disable-bootstrap (which of course is much faster):

• https://github.com/Rust-GCC/gccrs/blob/master/README.md
• https://github.com/Rust-GCC/gccrs/blob/master/.github/workflows/ccpp.yml
• https://github.com/Rust-GCC/gccrs/blob/master/Dockerfile

I think it's OK to keep it that way (I'm also doing that for my day-to-day development), but at least as a background task, we should also make sure that --enable-bootstrap works -- which it currently doesn't. I've produced a number of patches, that I'm going to submit individually.