gitlab-ci: try using an image with recent gcc _and_ python

.gitlab-ci.yml

@@ -1,7 +1,7 @@
 # Based on the GitLab example CI configuration
 
-# use the official gcc image, based on debian
-image: gcc
+# use an image which probably has an up-to-date gcc _and_ >=python3.6
+image: base/archlinux
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
@@ -9,8 +9,8 @@ variables:
 build:
   stage: build
   before_script:
-    - apt update
-    - apt -y install cmake ninja-build python3 ragel
+    - pacman --noconfirm -Sy
+    - pacman --noconfirm -S python3 gcc ninja cmake ragel git
   script: 
     - mkdir build && cd build
     - cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DLTO=ON -DTESTS=ON
@@ -24,8 +24,8 @@ build:
 test:
   stage: test
   before_script:
-    - apt update
-    - apt -y install cmake python3
+    - pacman --noconfirm -Sy
+    - pacman --noconfirm -S cmake ragel
   script:
     - cd build
     - ctest -vvv