Motivation for this change

• without this change the ninja builder driven by gn will use as many workers as the system has cores. Which may be greater than nix build-cores.

Things done

1. Verified load without patch exceeded expected by NIX_BUILD_CORES. Did not observe process count exceed expected.

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• 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 nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.