[PowerPC] Fix no-assert build

r212476 caused a compile failure (unused variable) in a non-assertion
build ...



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212477 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCISelLowering.cpp

@@ -4314,6 +4314,7 @@ PPCTargetLowering::LowerCall_64SVR4(SDValue Chain, SDValue Callee,
   }
 
   assert(NumBytesActuallyUsed == ArgOffset);
+  (void)NumBytesActuallyUsed;
 
   if (!MemOpChains.empty())
     Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, MemOpChains);