[DEVOPS-949] nix: Support building from git worktrees

[rvl]

Description

Previously it would fail to get the gitrev value:

error: illegal name: '.git'
(use '--show-trace' to show detailed location information)

You would have to supply a --argstr gitrev NNN manually to get it to work.

Linked issue

https://iohk.myjetbrains.com/youtrack/issue/DEVOPS-949

Type of change

• Bug fix to build system and dev environment.

QA Steps

git checkout develop
git worktree add ../csl/devops-949 devops-949-nix-git-worktree
cd ../csl/devops-949
nix-build -A cardano-sl-wallet-new-static
./result/bin/cardano-node --version

[angerman]

I'm not so happy about the amount of nix glue code we keep adding...

Don't see a way around it though either.

LGTM.

[rvl]

I'm not so happy about the amount of nix glue code we keep adding...

Me neither. We could move the problem into nixpkgs by upstreaming the fix. :-) Or add a nix builtin.
It will be good to delete this code, but in the meantime this will solve a usability bug.

[disassembler]

I've had this problem since I started here, but haven't worried about it, I just added an arg override for gitrev. This looks good to me! I also think we should upstream it.