###### Motivation for this change
fixes#51825
###### Things done
<!-- Please check what applies. Note that these are not hard requirements but merely serve as information for reviewers. -->
- [x] Tested using sandboxing ([nix.useSandbox](http://nixos.org/nixos/manual/options.html#opt-nix.useSandbox) on NixOS, or option `sandbox` in [`nix.conf`](http://nixos.org/nix/manual/#sec-conf-file) on non-NixOS)
- Built on platform(s)
- [x] NixOS
- [ ] macOS
- [ ] other Linux distributions
- [ ] Tested via one or more NixOS test(s) if existing and applicable for the change (look inside [nixos/tests](https://github.com/NixOS/nixpkgs/blob/master/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/`)
- [ ] Determined the impact on package closure size (by running `nix path-info -S` before and after)
- [ ] Assured whether relevant documentation is up to date
- [x] Fits [CONTRIBUTING.md](https://github.com/NixOS/nixpkgs/blob/master/.github/CONTRIBUTING.md).
---
- Fix GOPATH checks
- Install manpages
- Also build and install discovery and relay servers + cli
- Make the build more pure by explicitly setting the build username/host
The systemd files included with syncthing are "library" and not
"configuration" units, so they should be placed in lib/systemd
rather than etc/systemd, so that they can be customised by creating
unit files in etc/. This also corresponds to how syncthing's own
build script installs them.
The hack used here is shamelessly stolen from buildGoPackage. If it is
going to be applied to more expressions, it may make sense to factor it
out so it can be shared.
Currently only for the user services as NixOS handles the named system
instances slightly differently.
syncthing and syncthing-inotify are done the same way.
There are 4 parts to this:
1) Copy in the upstream unit files
2) Make the nixos module use the definition from upstream
3) Enable restarting of all instances (system and user) on resume
4) Allow the traffic in the firewall on default ports if wanted
fixes#18973
