Add GitLab CI support

• Add compile step via GitLab CI on docker:stretch container to check for compilation errors.

.gitlab-ci.yml

+image: debian:stretch
+
+before_script:
+  - dpkg --add-architecture i386
+  - apt-get update
+  - apt-get install libx11-dev:i386 libc6-dev-i386 build-essential  -y
+
+smoke-test-by-make:
+  stage: build
+  script:
+    - make
+  tags:
+    - docker