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>
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/145479
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions