[C++] fix tests for c++17 (nodiscard)

Author: Egor Seredin

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

@@ -74,23 +74,23 @@ class SbeMarketDataCodecBench : public CodecBench<SbeMarketDataCodecBench>
 
         marketData_.wrapForDecode((char *)buffer, messageHeader_.encodedLength(), actingBlockLength, actingVersion, bufferLength);
 
-        marketData_.transactTime();
-        marketData_.eventTimeDelta();
-        marketData_.matchEventIndicator();
+        (void)marketData_.transactTime();
+        (void)marketData_.eventTimeDelta();
+        (void)marketData_.matchEventIndicator();
 
         MarketDataIncrementalRefreshTrades::MdIncGrp &mdIncGrp = marketData_.mdIncGrp();
         while (mdIncGrp.hasNext())
         {
             mdIncGrp.next();
-            mdIncGrp.tradeId();
-            mdIncGrp.securityId();
-            mdIncGrp.mdEntryPx().mantissa();
-            mdIncGrp.mdEntrySize().mantissa();
-            mdIncGrp.numberOfOrders();
-            mdIncGrp.mdUpdateAction();
-            mdIncGrp.rptSeq();
-            mdIncGrp.aggressorSide();
-            mdIncGrp.mdEntryType();
+            (void)mdIncGrp.tradeId();
+            (void)mdIncGrp.securityId();
+            (void)mdIncGrp.mdEntryPx().mantissa();
+            (void)mdIncGrp.mdEntrySize().mantissa();
+            (void)mdIncGrp.numberOfOrders();
+            (void)mdIncGrp.mdUpdateAction();
+            (void)mdIncGrp.rptSeq();
+            (void)mdIncGrp.aggressorSide();
+            (void)mdIncGrp.mdEntryType();
         }
 
         return MessageHeader::encodedLength() + marketData_.encodedLength();

sbe-tool/src/test/cpp/CodeGenTest.cpp

@@ -591,7 +591,7 @@ struct CallbacksForEach
     void operator()(Car::FuelFigures& fuelFigures)
     {
         countOfFuelFigures++;
-        fuelFigures.usageDescription();
+        (void)fuelFigures.usageDescription();
     }
 
     void operator()(Car::PerformanceFigures& performanceFigures)