[Bug libstdc++/91067] [9/10 Regression] Clang compiler can't link executable if std::filesystem::directory_iterator is encountered

[ostash at ostash dot kiev.ua]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91067

--- Comment #17 from Viktor Ostashevskyi <ostash at ostash dot kiev.ua> ---
Ok, got following today with GCC 9.2 with "-O2 -fno-inline -flto=20":

ld.bfd: /tmp/tests.oKru4z.ltrans32.ltrans.o: in function
`std::__shared_ptr<void,
(__gnu_cxx::_Lock_policy)2>::operator=(std::__shared_ptr<void,
(__gnu_cxx::_Lock_policy)2>&&)':
c++/9.2.0/bits/shared_ptr_base.h:1265: undefined reference to
`std::__shared_ptr<std::filesystem::_Dir,
(__gnu_cxx::_Lock_policy)2>::__shared_ptr(std::__shared_ptr<std::filesystem::_Dir,
(__gnu_cxx::_Lock_policy)2>&&)'

Code base is huge, so it is hard to minimize test case. Even not sure whether
LTO or libstdc++ is guilty.