internal/rosa: fix up dependencies

These are no longer provided by the (incomplete) toybox implementations, so they need to be specified explicitly.

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

internal/rosa/libxml2.go

@@ -13,6 +13,9 @@ func (t Toolchain) newLibxml2() pkg.Artifact {
 	)
 	return t.New("libxml2-"+version, 0, []pkg.Artifact{
 		t.Load(Make),
+		t.Load(Gawk),
+		t.Load(Coreutils),
+		t.Load(Diffutils),
 		t.Load(XZ),
 	}, nil, nil, `
 cd /usr/src/