meson.build: Skip C++ detection unless we're targeting Windows The only C++ code that we currently still have in the repository is the code in qga/vss-win32/ - so we can skip the C++ detection unless we are compiling binaries for Windows. Message-Id: <20230705133639.146073-1-thuth@redhat.com> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Signed-off-by: Thomas Huth <thuth@redhat.com>