[Bug libstdc++/83279] std::experimental::filesystem::copy_file can't copy larger files than 2.0GiB

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83279

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
What does this output, for both gcc-5 and gcc-7?

#include <iostream>
int main()
{
  std::cout << "Large file support: "
#ifdef _GLIBCXX_USE_LFS
    "enabled"
#else
    "disabled"
#endif
  "\n";
}