In 4b8222983f (Cygwin: fix errno values set by readlinkat, 2023-04-18)
the code of `readlinkat()` was adjusted to align the `errno` with Linux'
behavior.

To accommodate for that, the `gen_full_path_at()` function was modified,
and the caller was adjusted to expect either `ENOENT` or `ENOTDIR` in
the case of an empty `pathname`, not just `ENOENT`.

However, `readlinkat()` is not the only caller of that helper function.

And while most other callers simply propagate the `errno` produced by
`gen_full_path_at()`, two other callers also want to special-case empty
`pathnames` much like `readlinkat()`: `fchmodat()` and `fstatat()`.

Therefore, these two callers need to be changed to expect `ENOTDIR` in
case of an empty `pathname`, too.

I noticed this issue when one of my workflows failed consistently
while trying to untar an archive containing a symbolic link and
claiming this:

    Cannot change mode to rwxr-xr-x: Not a directory

With this here fix, things start working as expected again.

Fixes: 4b8222983f (Cygwin: fix errno values set by readlinkat, 2023-04-18)
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Submitted-As: https://inbox.sourceware.org/cygwin-patches/072b5c57a76c935d79a321526e0c60a1383d22c4.1688484863.git.johannes.schindelin@gmx.de
In-Reply-To: https://inbox.sourceware.org/cygwin-patches/c985ab15b28da4fe6f28da4e20236bc0feb484bd.1687898935.git.johannes.schindelin@gmx.de