adns: explicitly disable parallel building
adns: explicitly disable parallel building

Fixing parallelism needs to get cross-header dependency right:
  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=51329

Let's disable parallelism on this package until upstream comes up
with a fix.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs