feat: port gcc to MontaukOS

toolchain/README.md

@@ -64,6 +64,20 @@ toolchain/
 
 ## Native binutils (runs on MontaukOS)
 
+The whole native SDK (binutils + GCC below, staged for the OS image) is
+built by one idempotent script — this is what a fresh clone should run:
+
+```bash
+make sdk          # from the repo root; wraps toolchain/build-native-sdk.sh
+```
+
+It invokes build-montauk-toolchain.sh first (cross compiler + sysroot),
+applies the host-build fix-ups listed under "Host-build gotchas", and
+strips the staged binaries. To force a rebuild after libc changes:
+`rm -rf toolchain/native toolchain/native-gcc toolchain/build/binutils-native
+toolchain/build/gcc-native` and re-run. The manual steps below are kept
+as a reference for what the script does.
+
 Binutils can be cross-compiled to run *on* MontaukOS itself
 (`--host=x86_64-montauk`), the first step toward a self-hosted GCC: