gitlab: 11.10.8 -> 12.0.3

This is a major version bump but things were generally straightforward
save two wrinkles:

 * it is necessary to ignore collisions in the gitlab bundler
   environment as both `omniauth_oauth2_generic` and
   `apollo_upload_server` provide a `console` executable.

 * grpc had to be patched since its build system expects the `AR`
   environment variable to contain not just the path to `ar` but
   also the `rpc` flags (see the discussion in nixpkgs #63056).

pkgs/applications/version-management/gitlab/default.nix

@@ -4,11 +4,24 @@
 }:
 
 let
-  rubyEnv = bundlerEnv {
+  rubyEnv = bundlerEnv rec {
     name = "gitlab-env-${version}";
     inherit ruby;
     gemdir = ./rubyEnv- + "${if gitlabEnterprise then "ee" else "ce"}";
+    gemset =
+      let x = import (gemdir + "/gemset.nix");
+      in x // {
+        # grpc expects the AR environment variable to contain `ar rpc`. See the
+        # discussion in nixpkgs #63056.
+        grpc = x.grpc // {
+          patches = [ ./fix-grpc-ar.patch ];
+          dontBuild = false;
+        };
+      };
     groups = [ "default" "unicorn" "ed25519" "metrics" ];
+    # N.B. omniauth_oauth2_generic and apollo_upload_server both provide a
+    # `console` executable.
+    ignoreCollisions = true;
   };
 
   flavour = if gitlabEnterprise then "ee" else "ce";