Simplify the build infrastructure for creating shells etc. for xanthous,
including relying more heavily on stuff exposed in Depot anyway, using
shellFor in the shell.nix, and using the haskell.nix branch of all-hies
for a significantly simpler build. At some point the all-hies stuff will
likely want to be promoted up to //third_party, but for now it's
experimental enough that I don't want to bother other people with it.
Change-Id: I43830de73830fdc07d48af9b87d7930f59599532
Reviewed-on: https://cl.tvl.fyi/c/depot/+/890
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>
Reviewed-by: BuildkiteCI
CI doesn't have a nixpkgs channel (obvs), and we want to be able to
build from the depot tree, so reorder some stuff so we never depend on
nixpkgs
Change-Id: I99b513a3d7bcd64b6d167335856651e0ca66e33b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/734
