Build codegene to fix the build error

Summary:
This diff fixes the circle CI error introduced with a recent commit (https://github.com/facebook/react-native/commit/3d8b5a35f9ef2a1c1c3c974917dbc9abc79ba522).

Changelog: [internal]

Reviewed By: philIip

Differential Revision: D32516744

fbshipit-source-id: 522b6815f0486a5ec1c97cffc19fb6f7a5da2dbd

.circleci/config.yml

@@ -92,6 +92,12 @@ commands:
             - ~/.cache/yarn
           key: v4-yarn-cache-{{ arch }}-{{ checksum "yarn.lock" }}
 
+  build_codegen:
+    steps:
+      - run:
+          name: "Codegen: Build react-native-codegen package"
+          command: cd packages/react-native-codegen && yarn build
+
   install_buck_tooling:
     steps:
       - restore_cache:
@@ -367,6 +373,7 @@ jobs:
       - setup_artifacts
       - setup_ruby
       - run_yarn
+      - build_codegen
 
       - run: |
           cd packages/rn-tester