If a player decides to build a civic center, places a foundation, then deletes it to place it slightly differently, the rubble is spawned.
This rubble is visible in the fog of war to all players.
The fog of war is supposed to hide everything if it hadn't been explored prior, so do this.
Notice there are often only one or two places where a civic center is likely to be built, so it can be a critical giveaway to the enemy that might just want to build a civic center there too a minute later.
Notice the rubble isn't miraged, so it will be hidden completely in the fog of war, even if the entity has been explored prior.
But so are corpses and noone has complained about that yet. Also miraging corpses and rubble might be weird, since they are supposed to decay in some seconds, as opposed to resources and buildings.
The code is the exact same as rP16919, just without line ending mess.