Can you please explain how you generate the orig tarball? The right way to do it is just run `origtargz` befor you run any gbp command because that prevents gbp from generating it on its own.
The first of origtargz's strategies (pristine-tar) would have succeeded on libtcod. Instead of libtcod_1.24.0+dfsg.orig.tar.xz which is already in the archive you have uploaded libtcod_1.24.0+dfsg.orig.tar.gz which contains different content. I have generated a source pkg from git and have uploaded that.

