stupid constexpr tricks

You shouldn't expect this to compile, for several reasons, but it does.

https://compiler-explorer.com/z/sb1648Wrr

```cpp
constexpr auto make_val() {
  return 10;
}

int main()
{
  const auto x = 42;
  const auto y = [](){ return 43; }();

  const auto result = [](){
    return x + y + make_val();
  }();

  static_assert(result == 95);
}
```