It can’t be built on the fly, it’s what you get when you build the level, so I guess you would put it in source control.
This answer was the top result in my google search when I was researching whether to commit _BuiltData in source control and it’s incorrect, you can generate _BuildData on the fly.
In my case, I have a Jenkins pipeline to build the game so I build the map data with each job instead of committing it to source control.
The ResavePackages commandlet can be used to build map data (you can also hit “Build” in the editor):
"<path-to-ue4-binaries>\UE4Editor-Cmd.exe" "<path-to-project>.uproject" -Run=ResavePackages -IgnoreChangeList -BuildLighting -Quality=Production -MapsOnly -ProjectOnly -AllowCommandletRendering
Unfortunately, I couldn’t find any good documentation on the switches for the commandlet.