[Nix-dev] Override nix.maxJobs without editing hardware-configuration.nix?

[James Cook]

I can't set nix.maxJobs in configuration.nix, because it is set in
hardware-configuration.nix:

error: The unique option `nix.maxJobs' is defined multiple times, in
`/etc/nixos/hardware-configuration.nix' and
`/etc/nixos/configuration.nix'.

Of course, I could work around this by editing
hardware-configuration.nix, but then the change would be lost the next
time I run nixos-generate-config. Is there a better way to do this?

(Context: with hyperthreading, my laptop presents 8 cores, but doesn't
really have an appropriate amount of RAM for 8 simultaneous builds.)

Thanks,
  James