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/libffi.go

@@ -7,7 +7,7 @@ func (t Toolchain) newLibffi() pkg.Artifact {
 		version  = "3.4.5"
 		checksum = "apIJzypF4rDudeRoI_n3K7N-zCeBLTbQlHRn9NSAZqdLAWA80mR0gXPTpHsL7oMl"
 	)
-	return t.New("libffi-"+version, false, []pkg.Artifact{
+	return t.New("libffi-"+version, 0, []pkg.Artifact{
 		t.Load(Make),
 		t.Load(KernelHeaders),
 	}, nil, nil, `