`std::filesystem` fails to link

[glebm]

Attempting to use std::filesystem results in:

lld: error: undefined symbol: bool __cdecl std::__1::__fs::filesystem::__create_directories(class std::__1::__fs::filesystem::path const &, class std::__1::error_code *)

[thrimbor]

std::filesystem is not available unfortunately as at the time of porting libc++ had no working win32 backend for it.

It appears there has been Windows-related work in this area since then, but I haven't checked how complete it is, whether it'll work on nxdk or how much work it would be to get it going. This is further complicated by llvm having moved to a mono-repo in the meantime (see #3).