Add NIAI for exclusive write before CAS read barrier

Signed-off-by: Filip Jeremic <fjeremic@ca.ibm.com>

runtime/compiler/trj9/z/codegen/J9TreeEvaluator.cpp

@@ -9756,6 +9756,7 @@ static TR::Register *VMinlineCompareAndSwap(
       // Compare-And-Swap on object reference, while primarily is a store operation, it is also an implicit read (it 
       // reads the existing value to be compared with a provided compare value, before the store itself), hence needs
       // a read barrier
+      generateS390IEInstruction(cg, TR::InstOpCode::NIAI, 1, 0, node);
       generateRXYInstruction(cg, guardedLoadMnemonic, node, tempReadBarrier, generateS390MemoryReference(*casMemRef, 0, cg));
 
       cg->stopUsingRegister(tempReadBarrier);