internal/rosa: stage3 special case helper

This makes it cleaner to specify non-stage3 and stage3-exclusive dependencies.

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

internal/rosa/busybox.go

@@ -108,18 +108,15 @@ func (t Toolchain) NewBusybox() pkg.Artifact {
 		checksum = "Ial94Tnt7esJ_YEeb0AxunVL6MGYFyOw7Rtu2o87CXCi1TLrc6rlznVsN1rZk7it"
 	)
 
-	extra := []pkg.Artifact{
-		t.NewMake(),
-		t.NewKernelHeaders(),
-	}
 	var env []string
-
 	if t == toolchainStage3 {
-		extra = nil
 		env = append(env, "EXTRA_LDFLAGS=-static")
 	}
 
-	return t.New("busybox-"+version, extra, nil, slices.Concat([]string{
+	return t.New("busybox-"+version, stage3Concat(t, []pkg.Artifact{},
+		t.NewMake(),
+		t.NewKernelHeaders(),
+	), nil, slices.Concat([]string{
 		"ROSA_BUSYBOX_ENABLE=" + strings.Join([]string{
 			"STATIC",
 			"PIE",