Add a auto-sync workflow.

.github/workflows/sync-fork-parent.yaml

@@ -0,0 +1,25 @@
+name: Sync with upstream
+
+on:
+  schedule:
+    - cron: '1 1 * * *'
+  workflow_dispatch: # for manual triggering
+
+jobs:
+  sync:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/[email protected]
+        with:
+          repository: 'shenhanc78/llvm-project'
+          ref: 'main'
+          fetch-depth: 0 # fetch all history for accurate syncing
+      - name: Sync with upstream
+        uses: zhangnew/sync-upstream@v1
+        with:
+          username: 'Han Shen'
+          useremail: '[email protected]'
+          upstream: 'llvm/llvm-project'
+          upstream-branch: 'main'
+          branch: 'main'