This adds a way to control the deprecated features that need to be
enable while evaluating the specific nixpkgs version
Change-Id: Ia2b9a29f1966d4d5f32239a36ba8270330007da9
This avoids rebuilding Lix each time we need to modify the lib tests
(as flake.nix stays unchanged), and adds a way to control the deprecated
features that need to be enable while evaluating the nixpkgs lib
testsuite
Change-Id: I2baa1cf90effcaf9d53337c6a7a5b24d6297178c