[globalisel][tablegen] Fix an unused variable warning in release builds after r307133

llvm-svn: 307138

llvm/lib/CodeGen/GlobalISel/InstructionSelector.cpp

@@ -59,7 +59,7 @@ void InstructionSelector::executeEmitTable(NewMIVector &OutMIs,
       break;
     }
     case GIR_BuildMI: {
-      int64_t InsnID = *Command++;
+      int64_t InsnID LLVM_ATTRIBUTE_UNUSED = *Command++;
       int64_t Opcode = *Command++;
       assert((size_t)InsnID == OutMIs.size() &&
              "Expected to store MIs in order");