std::fs::remove_dir_all doesn't handle paths that are too long

[drrlvn]

On Linux unlink() might fail with ENAMETOOLONG but std::fs::remove_dir_all doesn't handle that and ignores the error, leaving the directory as it was.

When the path is too long a parent directory should be open()ed instead and unlinkat() should be called with the relative path.

[the8472]

It would be best to always use openat, otherwise there could be a race where the target directory is swapped with a symlink to some other directory and it then tries to delete descendants of the swapped one.