ci: Add clang-format check (google#132)

* ci: Add Clang-format check

* ci: Only check file(s) in the commit list

.github/workflows/Dockerfile

@@ -0,0 +1,5 @@
+# Create a virtual environment with all tools installed
+# ref: https://hub.docker.com/_/alpine
+FROM alpine:edge
+# Install system build dependencies
+RUN apk add --no-cache git clang

.github/workflows/clang_format.yml

@@ -0,0 +1,24 @@
+name: clang-format Check
+
+on: [push, pull_request]
+
+jobs:
+  # Building using the github runner environement directly.
+  clang-format:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Fetch origin/master
+      run: git fetch origin master
+    - name: List of changed file(s)
+      run: git diff --name-only FETCH_HEAD
+
+    - name: Build clang-format docker
+      run: cd .github/workflows && docker build --tag=linter .
+    - name: Check clang-format
+      run: docker run --rm --init -v $(pwd):/repo linter:latest clang-format --version
+    - name: clang-format help
+      run: docker run --rm --init -v $(pwd):/repo linter:latest clang-format --help
+
+    - name: Check current commit
+      run: docker run --rm --init -v $(pwd):/repo -w /repo linter:latest sh -c "git diff --name-only FETCH_HEAD | grep '\.c$\|\.h$\|\.cc$' | xargs clang-format --style=file --dry-run --Werror "