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/mksh.go

@@ -7,7 +7,7 @@ func (t Toolchain) newMksh() pkg.Artifact {
 		version  = "59c"
 		checksum = "0Zj-k4nXEu3IuJY4lvwD2OrC2t27GdZj8SPy4DoaeuBRH1padWb7oREpYgwY8JNq"
 	)
-	return t.New("mksh-"+version, false, stage3Concat(t, []pkg.Artifact{},
+	return t.New("mksh-"+version, 0, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Make),
 		t.Load(Perl),
 	), nil, []string{