[dev.power64] liblink: disable stack split for now

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/122460043

src/liblink/obj9.c

@@ -639,6 +639,9 @@ addstacksplit(Link *ctxt, LSym *cursym)
 static Prog*
 stacksplit(Link *ctxt, Prog *p, int32 framesize, int noctxt)
 {
+	// TODO(minux)
+	return p;
+
 	int32 arg;
 	Prog *q, *q1;