Comment 12 for bug 1824721

The -lstdc++fs requirement for std::filesystem in GCC 8 is documented in several places:

https://gcc.gnu.org/onlinedocs/gcc-8.3.0/libstdc++/manual/manual/using.html#manual.intro.using.flags
https://gcc.gnu.org/onlinedocs/gcc-8.3.0/libstdc++/manual/manual/status.html#status.iso.2017
https://gcc.gnu.org/onlinedocs/gcc-8.3.0/libstdc++/manual/manual/using_dynamic_or_shared.html#manual.intro.using.linkage.experimental

I don't know why it crashes with Ubuntu, it should be a linker error. I suspect Ubuntu is doing something silly like providing libstdc++.so from GCC 9, which defines std::filesystem::path differently, and so is not compatible with C++17 code compiled using GCC 8.