Add built-in nlohmann_json build to CI

.gitlab-ci.yml

@@ -102,7 +102,7 @@ variables:
 .geomodelvisualization-build-template: &geomodelvisualization-job
   stage: build
   variables:
-    CMAKE_ARGS: ${CMAKE_BASE_ARGS}
+    CMAKE_ARGS: ${CMAKE_BASE_ARGS} ${CMAKE_EXTRA_FLAGS}
   script:
     - echo "PWD; LS"
     - pwd; ls
@@ -163,3 +163,11 @@ geomodelvisualization-ubuntu:
   <<: *ubuntu-job
   <<: *geomodelvisualization-job
   needs: ["coin-ubuntu", "soqt-ubuntu", "geomodelcore-ubuntu", "geomodelio-ubuntu"]
+  
+geomodelvisualization-ubuntu-standalone:
+  <<: *ubuntu-job
+  <<: *geomodelvisualization-job
+  needs: ["coin-ubuntu", "soqt-ubuntu", "geomodelcore-ubuntu", "geomodelio-ubuntu"]
+  variables:
+    CMAKE_EXTRA_FLAGS: -DGEOMODEL_USE_BUILTIN_JSON=TRUE
+