Revert "Revert "Upgrade to 5.0.71.48"" DO NOT MERGE

This reverts commit f2e3994fa5148cc3d9946666f0b0596290192b0e,
and updates the x64 makefile properly so it doesn't break that
build.

FPIIM-449

Change-Id: Ib83e35bfbae6af627451c926a9650ec57c045605
(cherry picked from commit 109988c7ccb6f3fd1a58574fa3dfb88beaef6632)
diff --git a/src/compiler/int64-lowering.h b/src/compiler/int64-lowering.h
new file mode 100644
index 0000000..79a95dc
--- /dev/null
+++ b/src/compiler/int64-lowering.h
@@ -0,0 +1,63 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_COMPILER_INT64_REDUCER_H_
+#define V8_COMPILER_INT64_REDUCER_H_
+
+#include "src/compiler/common-operator.h"
+#include "src/compiler/graph.h"
+#include "src/compiler/machine-operator.h"
+#include "src/compiler/node-marker.h"
+#include "src/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+namespace compiler {
+
+class Int64Lowering {
+ public:
+  Int64Lowering(Graph* graph, MachineOperatorBuilder* machine,
+                CommonOperatorBuilder* common, Zone* zone,
+                Signature<MachineRepresentation>* signature);
+
+  void LowerGraph();
+
+ private:
+  enum class State : uint8_t { kUnvisited, kOnStack, kInputsPushed, kVisited };
+
+  struct Replacement {
+    Node* low;
+    Node* high;
+  };
+
+  Zone* zone() const { return zone_; }
+  Graph* graph() const { return graph_; }
+  MachineOperatorBuilder* machine() const { return machine_; }
+  CommonOperatorBuilder* common() const { return common_; }
+  Signature<MachineRepresentation>* signature() const { return signature_; }
+
+  void LowerNode(Node* node);
+  bool DefaultLowering(Node* node);
+
+  void ReplaceNode(Node* old, Node* new_low, Node* new_high);
+  bool HasReplacementLow(Node* node);
+  Node* GetReplacementLow(Node* node);
+  bool HasReplacementHigh(Node* node);
+  Node* GetReplacementHigh(Node* node);
+
+  Zone* zone_;
+  Graph* const graph_;
+  MachineOperatorBuilder* machine_;
+  CommonOperatorBuilder* common_;
+  NodeMarker<State> state_;
+  ZoneStack<Node*> stack_;
+  Replacement* replacements_;
+  Signature<MachineRepresentation>* signature_;
+};
+
+}  // namespace compiler
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_COMPILER_INT64_REDUCER_H_