distcc incorrectly claims that iquote parameter is not used with clang++ 16, breaking my -Werror build

[KrzaQ]

Here's a reproduction (tested on Arch Linux and Fedora 38)

% touch x.cpp && cat x.cpp
% clang++ --version
clang version 16.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
% which clang++
/usr/bin/clang++
% distcc --version
distcc 3.4 x86_64-pc-linux-gnu
  (protocols 1, 2 and 3) (default port 3632)
  built Aug  2 2023 06:24:08
Copyright (C) 2002, 2003, 2004 by Martin Pool.
Includes miniLZO (C) 1996-2002 by Markus Franz Xaver Johannes Oberhumer.
Portions Copyright (C) 2007-2008 Google.

distcc comes with ABSOLUTELY NO WARRANTY.  distcc is free software, and
you may use, modify and redistribute it under the terms of the GNU
General Public License version 2 or later.

Built with Zeroconf support.

Please report bugs to distcc@lists.samba.org

% clang++ -iquote . -c x.cpp
% distcc clang++ -iquote . -c x.cpp
clang-16: warning: argument unused during compilation: '-iquote .' [-Wunused-command-line-argument]