Issue description

According to #30072 it should now be possible to use nix-build to build a buildStackProject derivation. This however doesn't seem to work due to stack failing to download the resolver build plan:

Downloading lts-9.14 build plan ...
HttpExceptionRequest Request {
  host                 = "raw.githubusercontent.com"
  port                 = 443
  secure               = True
  requestHeaders       = []
  path                 = "/fpco/lts-haskell/master//lts-9.14.yaml"
  queryString          = ""
  method               = "GET"
  proxy                = Nothing
  rawBody              = False
  redirectCount        = 10
  responseTimeout      = ResponseTimeoutDefault
  requestVersion       = HTTP/1.1
}
 (ConnectionFailure Network.BSD.getProtocolByName: does not exist (no such protocol name: tcp))
builder for ‘/nix/store/yg3yi8655dmazr072f1pww8rvfa8zyd2-Test.drv’ failed with exit code 1

This is the same error as in #19526 from before the new buildStackProject, which was closed without a solution.

Pinging the participants of these two issues @ElvishJerricco @peti @mboes @vaibhavsagar @wizzup and @vklquevs

Steps to reproduce

• Create new stack project: stack new test && cd test
• Add a default.nix with the contents

with import <nixpkgs> {};
haskell.lib.buildStackProject {
  name = "test";
  src = ./.;
}

• Add the following to stack.yaml:

nix:
  enable: true
  shell-file: default.nix

• Build (with latest master): nix-build -I nixpkgs=$HOME/src/nixpkgs

Technical details

• system: "x86_64-linux"
• host os: Linux 4.9.61, NixOS, 18.03.git.e3ab8368c0 (Impala)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 1.11.15
• channels(infinisil): ""
• channels(root): "nixos-18.03pre119086.737b466031"
• nixpkgs: /cfg/nixpkgs