Make HashNode visible (pytorch#34045)

Summary:
HashNode and CompareNode are useful functions for hanlding jit::Node. This is to unblock pytorch/glow#4235.
Pull Request resolved: pytorch#34045

Reviewed By: houseroad

Differential Revision: D20184733

Pulled By: yinghai

fbshipit-source-id: 6c829f2f111a490fd2d85017475c1731cd97fb20

Author: Yinghai Lu

torch/csrc/jit/ir/node_hashing.h

@@ -5,11 +5,11 @@
 namespace torch {
 namespace jit {
 
-struct HashNode {
+struct TORCH_API HashNode {
   size_t operator()(const Node* k) const;
 };
 
-struct EqualNode {
+struct TORCH_API EqualNode {
   bool operator()(const Node* lhs, const Node* rhs) const;
 };