netintf.c includes sys/signal.h instead of signal.h, though that is far from recommendations. I believe that reason is ancient - some *nix where freeciv was developed in the 90's had some issue with signal.h (not yet standardised to that over sys/signal.h). Likely there's no reason to keep it that way 202x.
This issue affects void linux / musl build also in older branches - let's backport the fix. Old patch applies to S3_0. For S2_6 a new patch has been attached.
netintf.c includes sys/signal.h instead of signal.h, though that is far from recommendations. I believe that reason is ancient - some *nix where freeciv was developed in the 90's had some issue with signal.h (not yet standardised to that over sys/signal.h). Likely there's no reason to keep it that way 202x.