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/musl.go

@@ -41,16 +41,8 @@ rmdir -v /work/lib
 		script = ""
 	}
 
-	extra := []pkg.Artifact{
+	return t.New("musl-"+version, stage3Concat(t, attr.Extra,
 		t.NewMake(),
-	}
-	if t == toolchainStage3 {
-		extra = nil
-	}
-
-	return t.New("musl-"+version, slices.Concat(
-		attr.Extra,
-		extra,
 	), nil, slices.Concat([]string{
 		"ROSA_MUSL_TARGET=" + target,
 	}, attr.Env), `