LLVM Constant Value to c++ value

  auto llval = b.getInt32(-1);
  std::cout << llval->getZExtValue() << "\n";  // 无符号
  std::cout << llval->getSExtValue() << "\n";  // 有符号

  ConstantFP* llval = ConstantFP::get(*ctx, APFloat(1.2));
  std::cout << llval->getValueAPF().convertToDouble() << "\n";

  ConstantFP* llval = ConstantFP::get(*ctx, APFloat((float)1.2));
  std::cout << llval->getValueAPF().convertToFloat() << "\n";