[gccjit][ci] Enable code formatting checks in CI pipeline

.github/workflows/build.yml

@@ -2,6 +2,19 @@ name: Build
 on: [push, pull_request]
 
 jobs:
+  check-format:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install code formatters
+        run: |
+          sudo apt-get update
+          sudo apt-get install clang-format git
+
+      - name: Check code formatting
+        run: ./check-format.sh
+
   build:
     runs-on: ubuntu-24.04
     env:

check-format.sh

@@ -0,0 +1,10 @@
+#!/usr/bin/env bash
+
+set -eu
+
+diff=$(git clang-format -q --extensions c,cc,cpp,h,hpp --diff HEAD~1)
+if [[ -n diff ]]; then
+    # clang-format outputs some diff, which indicates the commit is not properly
+    # formatted.
+    exit 1
+fi