internal/rosa: early toybox variant

This is a variant of toybox with unfinished tools enabled, for artifacts that will end up in a dependency loop without them.

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

internal/rosa/mksh.go

@@ -10,6 +10,7 @@ func (t Toolchain) newMksh() pkg.Artifact {
 	return t.New("mksh-"+version, 0, stage3Concat(t, []pkg.Artifact{},
 		t.Load(Make),
 		t.Load(Perl),
+		t.Load(Coreutils),
 	), nil, []string{
 		"LDSTATIC=-static",
 	}, `