Fix decoder benchmark. (aeron-io#753)

Author: js-labs

sbe-benchmarks/src/main/cpp/SbeCarCodecBench.h

@@ -77,16 +77,16 @@ class SbeCarCodecBench : public CodecBench<SbeCarCodecBench>
  car.putModel(MODEL, MODELLEN);
 
  return car.encodedLength();
- };
+ }
 
  virtual std::uint64_t decode(const char *buffer, const std::uint64_t bufferLength)
  {
  car.wrapForDecode((char *)buffer, 0, Car::sbeBlockLength(), Car::sbeSchemaVersion(), bufferLength);
 
- int64_t tmpInt;
- const char *tmpChar;
- double tmpDouble;
- bool tmpBool;
+ volatile int64_t tmpInt;
+ volatile const char *tmpChar;
+ volatile double tmpDouble;
+ volatile bool tmpBool;
 
  tmpInt = car.serialNumber();
  tmpInt = car.modelYear();
@@ -139,7 +139,7 @@ class SbeCarCodecBench : public CodecBench<SbeCarCodecBench>
  (void)tmpBool;
 
  return car.encodedLength();
- };
+ }
 
 private:
  Car car;