message: Use MAKE_ENUM_HASHABLE to hash SymbolKind
diff: @@ -36,17 +36,7 @@ struct IndexVar;
  // front of others.
  enum class SymbolKind : uint8_t { Invalid, File, Type, Func, Var };
  MAKE_REFLECT_TYPE_PROXY(SymbolKind);
  -
  -// FIXME: Make old compiler happy.
  -namespace std {
  -template <>
  -struct hash<::SymbolKind> {
  - size_t operator()(const ::SymbolKind& instance) const {
  - using type = std::underlying_type<::SymbolKind>::type;
  - return std::hash<type>()(static_cast<type>(instance));
  - }
  -};
  -} // namespace std
  +MAKE_ENUM_HASHABLE(SymbolKind);
  using RawId = uint32_t;
  