Add CodeQL scanning.

.github/codeql.yml

@@ -0,0 +1,7 @@
+paths-ignore:
+  - 'test*.c'
+
+query-filters:
+  - exclude:
+      id: cpp/commented-out-code
+

.github/workflows/codeql.yml

@@ -0,0 +1,50 @@
+name: "CodeQL"
+
+on:
+  push:
+    branches: [ "master" ]
+  pull_request:
+    branches: [ "master" ]
+  schedule:
+    - cron: "46 3 * * 0"
+
+jobs:
+  analyze:
+    name: Analyze
+    runs-on: ubuntu-latest
+    permissions:
+      actions: read
+      contents: read
+      security-events: write
+
+    strategy:
+      fail-fast: false
+      matrix:
+        language: [ cpp ]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+        with:
+          submodules: recursive
+
+      - name: Update build environment
+        run: sudo apt-get update --fix-missing -y
+
+      - name: Install prerequisites
+        run: sudo apt-get install -y zlib1g-dev
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v2
+        with:
+          languages: ${{ matrix.language }}
+          config-file: ./.github/codeql.yml
+          queries: +security-and-quality
+
+      - name: Autobuild
+        uses: github/codeql-action/autobuild@v2
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v2
+        with:
+          category: "/language:${{ matrix.language }}"