CI: add debug messages to build script.

.gitlab-ci.yml

@@ -85,6 +85,8 @@ variables:
     - cmake --version
     - mkdir build
     - cd build
+    - echo "CMAKE_ARGS - ${CMAKE_ARGS}"
+    - echo "CMAKE_EXTRA_FLAGS - ${CMAKE_EXTRA_FLAGS}"
     - cmake ${CMAKE_ARGS} ${CMAKE_EXTRA_FLAGS} ..
     - cmake --build . -- -j2 # using too many threads will cause weird compilation errors on the Ubuntu docker images...
     - cmake --build . -- install