https://gerrit.libreoffice.org/c/core/+/145479

From a7a6b436f1a83321ccba5b6b44a275205aa729e0 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Fri, 13 Jan 2023 15:09:59 +0000
Subject: [PATCH] configure.ac: Fix build with --with-system-zxing and < Clang
 16

Clang 15 and older default to -std=c++14, not -std=c++17 (unlike Clang 16 onwards).

This doesn't show up with GCC because GCC 11 onwards defaults to -std=c++17.

The new version of libzxing requires C++ 17, per its release notes. Adapt
the configure check accordingly to pass -std=c++17 when checking for its
headers and save accordingly if successful.

(Do this via ${CXXFLAGS_CXX11} which has the appropriate switch
for our compiler, despite its name.)

Bug: https://bugs.gentoo.org/890324
Change-Id: Iaaa8fdc05eea0e26416b605bfda8f2d831f8729c
Signed-off-by: Sam James <sam@gentoo.org>
--- a/configure.ac
+++ b/configure.ac
@@ -11187,7 +11187,7 @@ else
                 continue
             fi
             dnl TODO: White space in $i would cause problems:
-            CXXFLAGS="$save_CXXFLAGS -I$i/ZXing"
+            CXXFLAGS="$save_CXXFLAGS ${CXXFLAGS_CXX11} -I$i/ZXing"
             AC_CHECK_HEADER(MultiFormatWriter.h, [ZXING_CFLAGS=-I$i/ZXing; break],
                 [unset ac_cv_header_MultiFormatWriter_h], [#include <stdexcept>])
         done
-- 
2.39.0