zug: fix build on darwin

The bazel configuration file `BUILD` conflicts with the build folder
that should be created. Its fine to just remove it since we are not
using bazel to build this package.

pkgs/by-name/zu/zug/package.nix

@@ -24,6 +24,9 @@ stdenv.mkDerivation rec {
   cmakeFlags = [
     "-Dzug_BUILD_EXAMPLES=OFF"
   ];
+  preConfigure = ''
+    rm BUILD
+  '';
   meta = with lib; {
     homepage    = "https://github.com/arximboldi/zug";
     description = "library for functional interactive c++ programs";