[build] Check for code generation on Darwin

Sadly, it can only be done inside macOS because
of how examples are generated.

circle.yml

@@ -221,6 +221,12 @@ commands:
           name: Prepare macOS
           command: |
             brew install cmake ccache glfw ninja pkgconfig qt
+      - run:
+          name: Code Generators macOS
+          command: |
+              platform/darwin/scripts/generate-style-code.js
+              platform/darwin/scripts/update-examples.js
+              git add -A && git diff --staged --exit-code
   next-config:
     parameters:
       config_params: