feat: add export symbol name test to CI for embedded targets

- Created _demo/embed/export/ with test for //export directive
- Test verifies symbols are exported with correct names (LPSPI2_IRQHandler, SysTick_Handler)
- Added CI workflow step to run the test
- Essential for embedded development where hardware requires specific symbol names

🤖 Generated with [codeagent](https://github.com/qbox/codeagent)
Co-authored-by: luoliwoshang <51194195+luoliwoshang@users.noreply.github.com>

.github/workflows/llgo.yml

@@ -133,6 +133,13 @@ jobs:
           chmod +x test.sh
           ./test.sh
 
+      - name: Test export symbol names for embedded targets
+        run: |
+          echo "Testing //export with different symbol names for embedded development..."
+          cd _demo/embed/export
+          chmod +x test.sh
+          ./test.sh
+
       - name: _xtool build tests
         run: |
           cd _xtool