netbsd: Generalize builder to any-bsd setup hook

[Ericson2314]

Motivation for this change

Do this to get ready for other BSDs.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[alyssais]

What's the point of netBSDSetupHook?

[Ericson2314]

What's the point of netBSDSetupHook?

I recall a few things did NETBSDSRCDIR and not just BSDSRCDIR (perhaps not intentionally). So I put that back.

[alyssais]

> What's the point of netBSDSetupHook? I recall a few things did `NETBSDSRCDIR` and not just `BSDSRCDIR` (perhaps not intentionally). So I put that back.

Hmm, do you have an example? I looked through the NetBSD sources and didn't see anywhere it was used outside a Makefile, and saw almost no use of make -e, so I'd be curious to know what needs it.

[alyssais]

Actually, I'm realising I don't understand how the builder works. Does bmake look at environment variables by default or something? How do all these things we export become Make variables?

[Ericson2314]

Oh good point! I used to put -e everywhere, but that broke things. So NETBSDSRCDIR must not actually be needed.

[Ericson2314]

Check out addMakeFlags for where some env vars are manually passed to make.