message: Fix use of variables only used in asserts.
  This otherwise triggers "unused variable" errors in optimized build mode.
diff: @@ -171,10 +171,14 @@ public:
  SDBMBuilderResult visitSum(SDBMSumExpr expr) {
  auto lhs = visit(expr.getLHS());
  auto rhs = visit(expr.getRHS());
  - for (auto pos : rhs.negativePos)
  + for (auto pos : rhs.negativePos) {
  + (void)pos;
  assert(pos == 0 && "unexpected variable on the RHS of SDBM sum");
  - for (auto pos : rhs.positivePos)
  + }
  + for (auto pos : rhs.positivePos) {
  + (void)pos;
  assert(pos == 0 && "unexpected variable on the RHS of SDBM sum");
  + }
  lhs.value += rhs.value;
  return lhs;
  