rm: give a sensible diagnostic when failing to remove a symlink

rm: give a sensible diagnostic when failing to remove a symlink

On some systems (those with openat et al), when rm would fail to
remove a symlink, it would fail with the misleading diagnostic,
"Too many levels of symbolic links".
* NEWS: Mention the bug fix.
* src/remove.c (is_nondir_lstat): New function.
(remove_entry): Use it to catch failed-to-remove symlink (and any
other non-dir) here so that we don't fall through and try to treat
it as directory, which -- with a symlink -- would provoke the bogus
ELOOP failure.
* tests/rm/fail-eacces: Add a test for the above.
* src/c99-to-c89.diff: Adjust offsets.