Use official gcc 9.2 multi-arch image

.gitlab-ci.yml

@@ -3,11 +3,7 @@ stages:
 
 .compile: &compile_tmpl
   stage: build
-  image: ubuntu:18.04
-  before_script:
-    - apt-get update
-        && apt-get install -y build-essential
-        && rm -rf /var/lib/apt/lists/*
+  image: gcc:9.2
 
   script:
     - make