internal/rosa: flags for toolchain-dependent artifact

This is much cleaner to add extra flags to.

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

internal/rosa/musl.go

@@ -42,7 +42,7 @@ rmdir -v /work/lib
 		script = ""
 	}
 
-	return t.New("musl-"+version, false, stage3Concat(t, attr.Extra,
+	return t.New("musl-"+version, 0, stage3Concat(t, attr.Extra,
 		t.Load(Make),
 		t.Load(Coreutils),
 	), nil, slices.Concat([]string{