Add CI to make sure the IDE is building on linux

.gitlab-ci.yml

+test:
+    before_script:
+        - install_clean_nightly.sh bundle-complete
+        - apt-get update -qq
+        - apt-get install -y -qq build-essential
+    image: "camilstaps/clean:nightly"
+    script:
+        - clm -nt -nr -h 67108864 -s 5242880 -IL ArgEnv -IL StdLib -IL Directory -I Pm -I Unix -I Util -I BatchBuild -I Interfaces/LinkerInterface -I cpm/Posix -I cpm Cpm -o cpm/cpm
+        - cpm CpmLinux.prj --force
+    artifacts:
+        paths:
+            - "cpm/cpm"