add code-coverage workflow

.github/workflows/code-coverage.yml

@@ -0,0 +1,18 @@
+name: Code coverage
+on: [push, pull_request]
+jobs:
+  run:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+      - name: Build
+        run: make LLAMA_CODE_COVERAGE=1 all
+      - name: Run tests
+        run: |
+            make test
+            make coverage
+      - name: Upload coverage to Codecov
+        uses: codecov/codecov-action@v3
+        with:
+          files: lcov-report/coverage.info