[gitlab-ci] Add .gitlab-ci.yml, currently only with smoke-test stage

.gitlab-ci.yml

+image: "flowdalic/debian-dev:1.11"
+
+before_script:
+  - apt-get update && apt-get install -y nasm
+  - apt-get install -y -t testing valgrind
+  - |
+    TOOLS="cc c++ clang clang++ gcc g++ clang-tidy clang meson nasm include-what-you-use valgrind"
+    for tool in $TOOLS; do
+      echo "$tool version"
+      $tool --version
+    done
+
+stages:
+  - smoke-test
+
+smoke-test:
+  stage: smoke-test
+  script: make smoke-test