GH Actions: Add check that source code is formatted (by clang-format)

Issue #395 (bdwgc).

.github/workflows/clang-format-check.yml

@@ -0,0 +1,20 @@
+# Workflow for checking that source code is formatted by clang-format.
+name: clang-format check
+
+on: [ push, pull_request ]
+
+jobs:
+  build:
+    name: Check by clang-format
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Show clang-format version
+      run: >
+        clang-format --version
+    - name: Perform checking by clang-format
+      run: >
+        find . -iname '*.c' -o -iname '*.cc' -o -iname '*.cpp' -o -iname '*.h'
+        | xargs clang-format --dry-run --Werror