Change compiler to clang

.gitlab-ci.yml

@@ -26,9 +26,11 @@ build-job:       # This job runs in the build stage, which runs first.
     - linux
   before_script:
     - apt update
-    - apt install -y build-essential cmake libgtkmm-3.0-dev clang-tidy
+    - apt install -y clang cmake libgtkmm-3.0-dev clang-tidy
   script:
     - echo "Configuring"
+    - export CC=/usr/bin/clang
+    - export CXX=/usr/bin/clang++
     - cmake -B build .
     - echo "Building"
     - cmake --build build