ATLINFR-4161, ATLINFR-4147: Update to lwtnn v2.12

This updates lwtnn to v2.12. I need @ivivarel to move the files into the right place. You can get the version we need with

wget https://github.com/lwtnn/lwtnn/archive/refs/tags/v2.12.tar.gz

I suspect that this is only needed in master: the main reason for the update is to build with gcc11.