Add NixOS support

[jaroeichler]

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Description

Use nix-ld to run Bazel.

Fixes #1229

Type of change

Please delete options that aren't relevant.

• [x] New feature (non-breaking change which adds functionality)
• [x] This change requires a documentation update

How Has This Been Tested?

Used a pretty minimal system configuration and Bazel test ... passes 51 of 52 tests, integration_tests/running_actions_manager_test fails.

Checklist

• [x] Updated documentation if needed
• [ ] Tests added/amended
• [ ] bazel test //... passes locally
• [x] PR is contained in a single commit, using git amend see some docs

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This change is 

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All committers have signed the CLA.

[jaroeichler]

services.envfs.enable is only needed for some scripts that need /bin/bash. Is there a better way?

@SpamDoodler can you please check if this works on your system? I've made a few changes to what we've tried a few days ago. In particular, it works without NIX_CC_USE_RESPONSE_FILE=0 on a pretty minimal system configuration.

[jaroeichler]

Sure, adjusted the nixos flake module path to the darwin flake module path

[jaroeichler]

@aaronmondal Thanks, didn't notice it when reviewing the diff. Should be fine now.