The Rust `build` stage previously ran the entire compiler under QEMU x86_64
emulation on the arm64 builder. That was ~15x slower (one crate took >20 min)
and the emulated gcc/linker intermittently SIGSEGV'd or hung mid-link
(observed again building v0.5.2).
Pin the stage to $BUILDPLATFORM (native arm64 on Apple Silicon, amd64 in CI)
and cross-compile to x86_64-unknown-linux-musl with cargo-zigbuild — zig cc
supplies the musl sysroot + linker. rustc runs natively; no emulation. Build
drops from ~30 min to a few minutes and is deterministic. Output is the same
fully static musl binary (verified: x86_64, not a dynamic executable, 0
OpenSSL strings).
Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
