feat(nixos): add overlay for stdenv with mold linker

Author: takeokunn

nixos/config/nix.nix

@@ -3,4 +3,10 @@
     settings.cores = 8;
     optimise.automatic = true;
   };
+
+  nixpkgs.overlays = [
+    (final: prev: {
+      stdenv = prev.stdenvAdapters.useMold prev.stdenv;
+    })
+  ];
 }