internal/rosa: standard toolchain via 2-stage bootstrap

This implements the 2-stage bootstrap build without clumping the stages together in the cmake target.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/rosa.go

@@ -111,6 +111,14 @@ const (
 	// toolchainStage3 denotes the Gentoo stage3 toolchain. Special care must be
 	// taken to compile correctly against this toolchain.
 	toolchainStage3
+
+	// toolchainIntermediate denotes the intermediate toolchain compiled against
+	// toolchainStage3. This toolchain should be functionally identical to [Std]
+	// and is used to bootstrap [Std].
+	toolchainIntermediate
+
+	// Std denotes the standard Rosa OS toolchain.
+	Std
 )
 
 // lastIndexFunc is like [strings.LastIndexFunc] but for [slices].
@@ -203,6 +211,35 @@ ln -vs ../usr/bin /work/bin
 			"/usr/bin",
 			"/usr/lib/llvm/21/bin",
 		)
+
+	case toolchainIntermediate, Std:
+		boot := t - 1
+		musl, compilerRT, runtimes, clang := boot.NewLLVM()
+		support = slices.Concat([]pkg.Artifact{
+			cureEtc{},
+			musl,
+			compilerRT,
+			runtimes,
+			clang,
+			boot.NewBusybox(),
+		}, extra)
+		env = fixupEnviron(env, []string{
+			EnvTriplet + "=" + triplet(),
+			lcMessages,
+
+			// autotools projects act up with CFLAGS
+			"CC=clang " + cflags,
+			EnvRefCFLAGS + "=" + cflags,
+			"CXX=clang++ " + cxxflags(),
+			EnvRefCXXFLAGS + "=" + cxxflags(),
+			ldflags(false),
+
+			"AR=ar",
+			"RANLIB=ranlib",
+			"LIBCC=/system/lib/clang/21/lib/" + triplet() +
+				"/libclang_rt.builtins.a",
+		}, "/system/bin", "/bin")
+
 	default:
 		panic("unsupported toolchain " + strconv.Itoa(int(t)))
 	}