When visiting buffers that represent home-manager or nixos modules, set
compile-command to the relevant switch command.
Change-Id: I565e092d1e6b97eb7fee9d88211c0ee6ebb30b53
Reviewed-on: https://cl.tvl.fyi/c/depot/+/846
Reviewed-by: glittershark <grfn@gws.fyi>