drm_hwcomposer: Add pass/fail CI step for clang format-diff

Signed-off-by: Stefan Schake <stschake@gmail.com>
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
new file mode 100644
index 0000000..144eb2e
--- /dev/null
+++ b/.gitlab-ci.yml
@@ -0,0 +1,18 @@
+image: ubuntu:16.04
+
+before_script:
+  - apt-get --quiet update --yes >/dev/null
+  - apt-get --quiet install --yes clang-format-3.5 git >/dev/null
+
+stages:
+  - style
+
+clang-format:
+  stage: style
+  script:
+    - git diff -U --no-color master...HEAD | clang-format-diff-3.5 -p 1 -style=file > format-fixup.patch
+    - if [ -s format-fixup.patch ]; then cat format-fixup.patch && exit 1; fi
+  artifacts:
+    when: on_failure
+    paths:
+      - format-fixup.patch