google-cloud-cpp: schedule on big-parallel machines

This time for real I hope, not like around 07310e59a6.
Otherwise it often takes 1-2 hours on Hydra, which seems unnecessary.

pkgs/development/libraries/google-cloud-cpp/default.nix

@@ -122,6 +122,8 @@ stdenv.mkDerivation rec {
     "-DGOOGLE_CLOUD_CPP_ENABLE=${lib.concatStringsSep ";" apis}"
   ];
 
+  requiredSystemFeatures = [ "big-parallel" ];
+
   meta = with lib; {
     license = with licenses; [ asl20 ];
     homepage = "https://github.com/googleapis/google-cloud-cpp";