Fix unordered-map-over-enum for GCC 5.4 (pytorch#41063)

Summary:
Forgot to add this to pytorch#41055

Pull Request resolved: pytorch#41063

Differential Revision: D22407451

Pulled By: malfet

fbshipit-source-id: 6f06653b165cc4817d134657f87caf643182832a

Author: malfet

torch/csrc/jit/codegen/cuda/lower_thread_predicate.cpp

@@ -8,7 +8,7 @@ namespace torch {
 namespace jit {
 namespace fuser {
 
-const static std::unordered_map<ParallelType, int> pt_to_offset{
+const static std::unordered_map<ParallelType, int, TypeHash> pt_to_offset{
     {ParallelType::BIDx, 0},
     {ParallelType::BIDy, 1},
     {ParallelType::BIDz, 2},