[Bug bootstrap/67066] libstdc++-v3/src/filesystem/dir.cc fails to compile, preventing bootstrapping with libstdcxx-filesystem-ts

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67066

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Don't use --enable-concept-checks

It enforces C++03 semantics, so doesn't really make much sense these days.
Maybe I'll remove the option.