https://github.com/gulrak/filesystem#git-submodule-and-cmake says it should be off when used as a submodule, but it's actually always on :p https://github.com/gulrak/filesystem/blob/cd6805e94dd5d6346be1b75a54cdc27787319dd2/CMakeLists.txt#L18
https://github.com/gulrak/filesystem#git-submodule-and-cmake says it should be off when used as a submodule, but it's actually always on :p
filesystem/CMakeLists.txt
Line 18 in cd6805e