I think there's some undefined behavior in minisat/minisat.c that happens to work out OK in most circumstances but that may cause problems down the line, especially with link-time optimization. We have a downstream bug report about the problem here,
https://bugs.gentoo.org/863047 and I posted a patch there that hacks the types in minisat.c to make the warnings/errors go away. Not sure if it's the best fix, but it provides some evidence that we've diagnosed the right problem.
