The script build-webkit caches the parameters passed to it in order to clean the CMake cache if the developer changes those from one invocation to the next one.

The issue is that we support passing parameters also via the environment variable BUILD_WEBKIT_ARGS (which we use on the bots)
But we are not checking the values from this env var when deciding to clean the cache or not.

So it happens that if you change this environment variable with new values the CMake cache will not be clean automatically.