[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 #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No, I didn't just fix the error code, the code will copy files larger than 2G
now.

I assume your 5.4 build doesn't use sendfile, so doesn't have the 2G limitation
of sendfile.