Add support for XMM registers in SSA code generation pipeline.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index 235bf83baa5efa17573b9444507f70e9d51906a1..710d0583ba06ff6e7615d6aae85352f056aaf221 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -60,6 +60,8 @@ class FlowGraph: public ZoneAllocated {
     return graph_entry_;
   }
 
+  intptr_t alloc_ssa_temp_index() { return current_ssa_temp_index_++; }
+
   // Operations on the flow graph.
   void ComputeSSA();
   void ComputeUseLists();
@@ -96,7 +98,6 @@ class FlowGraph: public ZoneAllocated {
   void MarkLivePhis(GrowableArray<PhiInstr*>* live_phis);
 
   intptr_t current_ssa_temp_index() const { return current_ssa_temp_index_; }
-  intptr_t alloc_ssa_temp_index() { return current_ssa_temp_index_++; }
 
   // DiscoverBlocks computes parent_ and assigned_vars_ which are then used
   // if/when computing SSA.