Reland "[turbofan] Fix select lowering" with fix.

src/compiler/select-lowering.h

Index: src/compiler/select-lowering.h
diff --git a/src/compiler/select-lowering.h b/src/compiler/select-lowering.h
index ae22cade84420584cd21bb41140b343c51213c33..05ea0e0c75869c8063362cef35276fbb70491daf 100644
--- a/src/compiler/select-lowering.h
+++ b/src/compiler/select-lowering.h
@@ -28,8 +28,10 @@ class SelectLowering FINAL : public Reducer {
   Reduction Reduce(Node* node) OVERRIDE;
 
  private:
-  typedef std::map<Node*, Node*, std::less<Node*>,
-                   zone_allocator<std::pair<Node* const, Node*>>> Merges;
+  typedef std::multimap<Node*, Node*, std::less<Node*>,
+                        zone_allocator<std::pair<Node* const, Node*>>> Merges;
+
+  bool ReachableFrom(Node* const sink, Node* const source);
 
   CommonOperatorBuilder* common() const { return common_; }
   Graph* graph() const { return graph_; }