[Bug libstdc++/71004] recursive_directory_iterator does not have a user-provided default ctor

[eric at efcs dot ca]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71004

--- Comment #1 from Eric Fiselier <eric at efcs dot ca> ---
Additionally this seems to be affecting the value returned from
"recursion_pending()". The following code compiles and runs without asserting
on my machine.

#include <experimental/filesystem>
#include <cassert>

using namespace std::experimental::filesystem;

int main() {
    recursive_directory_iterator it;
    assert(it.recursion_pending() == false);
    assert(it.recursion_pending() == true);
}