message: fix nonnull metadata var name
diff: @@ -1211,13 +1211,22 @@ public:
  }
  AssumeVal::Kind op;
  + const char *str = nullptr;
  switch (ID) {
  - case LLVMContext::MD_nonnull: op = AssumeVal::NonNull; break;
  - case LLVMContext::MD_range: op = AssumeVal::Range; break;
  + case LLVMContext::MD_nonnull:
  + op = AssumeVal::NonNull;
  + str = "_nonnull";
  + break;
  + case LLVMContext::MD_range:
  + op = AssumeVal::Range;
  + str = "_range";
  + break;
  + default:
  + UNREACHABLE();
  }
  auto assume
  - = make_unique<AssumeVal>(i.getType(), i.getName() + "_range", i,
  + = make_unique<AssumeVal>(i.getType(), i.getName() + str, i,
  std::move(args), op);
  Fn.rauw(i, *assume);
  replace_identifier(llvm_i, *assume);
  