[Bug libstdc++/101510] std::filesystem::create_directory on an existing symlink to a directory

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101510

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I've added tests to verify that the behaviour is correct, and those tests pass
with all versions of GCC.