[Bug libstdc++/90299] std::filesystem::absolute("") and std::filesystem::absolute("", ec) behave differently

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90299

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Although that suggests I should report the error as errc::invalid_argument not
errc::no_such_file_or_directory.