Embed 64 bit constants directly in the IR, using two slots.

Contributed by Peter Cawley.

src/lj_opt_sink.c

@@ -220,6 +220,8 @@ static void sink_sweep_ins(jit_State *J)
   for (ir = IR(J->cur.nk); ir < irbase; ir++) {
     irt_clearmark(ir->t);
     ir->prev = REGSP_INIT;
+    if (irt_is64(ir->t) && ir->o != IR_KNULL)
+      ir++;
   }
 }