Essentially the same as for nixos, so I can get whitby to compile stuff
for me. Eventually I'll generalize this so things aren't as hardcoded to
my particular setup, but for now I'm the only one in the depot who's
using home-manager so this should be fine.
Change-Id: I1cb0344f5a11eea68bddc98976999c0928dfa84e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/937
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>
