internal/rosa: rename stage0 toolchain

This is stage0 relative to Rosa OS, and stage3 relative to the toolchain it is compiled on (Gentoo in this case). Referring to the toolchain itself as stage3 is counterintuitive and misleading.

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

internal/rosa/llvm.go

@@ -160,7 +160,7 @@ ln -s ld.lld /work/system/bin/ld
 			[2]string{"LIBCXX_USE_COMPILER_RT", "ON"},
 		)
 
-		if t > toolchainStage3 {
+		if t > toolchainStage0 {
 			// libcxxabi fails to compile if c++ headers not prefixed in /usr
 			// is found by the compiler, and doing this is easier than
 			// overriding CXXFLAGS; not using mv here to avoid chown failures
@@ -199,7 +199,7 @@ cp -r /system/include /usr/include && rm -rf /system/include
 
 		Paths: attr.paths,
 		Flag:  TExclusive,
-	}, stage3Concat(t, attr.extra,
+	}, stage0Concat(t, attr.extra,
 		t.Load(Libffi),
 		t.Load(Python),
 		t.Load(Perl),
@@ -233,7 +233,7 @@ func (t Toolchain) newLLVM() (musl, compilerRT, runtimes, clang pkg.Artifact) {
 	}
 
 	compilerRT = t.newLLVMVariant("compiler-rt", &llvmAttr{
-		env: stage3ExclConcat(t, []string{},
+		env: stage0ExclConcat(t, []string{},
 			"LDFLAGS="+earlyLDFLAGS(false),
 		),
 		cmake: [][2]string{
@@ -276,7 +276,7 @@ ln -s \
 
 	musl = t.NewMusl(&MuslAttr{
 		Extra: []pkg.Artifact{compilerRT},
-		Env: stage3ExclConcat(t, []string{
+		Env: stage0ExclConcat(t, []string{
 			"CC=clang",
 			"LIBCC=/system/lib/clang/21/lib/" +
 				triplet() + "/libclang_rt.builtins.a",
@@ -288,7 +288,7 @@ ln -s \
 	})
 
 	runtimes = t.newLLVMVariant("runtimes", &llvmAttr{
-		env: stage3ExclConcat(t, []string{},
+		env: stage0ExclConcat(t, []string{},
 			"LDFLAGS="+earlyLDFLAGS(false),
 		),
 		flags: llvmRuntimeLibunwind | llvmRuntimeLibcxx | llvmRuntimeLibcxxABI,
@@ -308,7 +308,7 @@ ln -s \
 
 	clang = t.newLLVMVariant("clang", &llvmAttr{
 		flags: llvmProjectClang | llvmProjectLld,
-		env: stage3ExclConcat(t, []string{},
+		env: stage0ExclConcat(t, []string{},
 			"CFLAGS="+earlyCFLAGS,
 			"CXXFLAGS="+earlyCXXFLAGS(),
 			"LDFLAGS="+earlyLDFLAGS(false),