message: Change trait verification to support older clang & gcc.
  This was resulting in an error:
  explicit specialization of 'BaseProperties' in class scope
  pre clang-7.0 (C++ DR 275).
diff: @@ -939,13 +939,7 @@ private:
  }
  };
  - template <typename First> struct BaseVerifier<First> {
  - static bool verifyTrait(const Instruction *op) {
  - return First::verifyTrait(op);
  - }
  - };
  -
  - template <> struct BaseVerifier<> {
  + template <typename...> struct BaseVerifier {
  static bool verifyTrait(const Instruction *op) { return false; }
  };
  @@ -959,13 +953,7 @@ private:
  }
  };
  - template <typename First> struct BaseProperties<First> {
  - static AbstractOperation::OperationProperties getTraitProperties() {
  - return First::getTraitProperties();
  - }
  - };
  -
  - template <> struct BaseProperties<> {
  + template <typename...> struct BaseProperties {
  static AbstractOperation::OperationProperties getTraitProperties() {
  return 0;
  }
  