A bug was reported to upstream dealing with large numbers (the test lgint fails) a := 2 ^63 b := -a write(b) Displays garbage output. The problem was due with gcc 9 (and later) optimizations. Reproducible: Always Steps to Reproduce: Known upstream bug with GCC 9.x and later. Upstream has the patch
I'm the proxied maintainer for this package, so you can assign the ticket to me. I already have the patches for this from upstream.
Fixed in icon-9.5.20h which is now in portage