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).