Warnings in CI system

Currently, CI logs are massively spammed with warnings. While with any other project, I would just go for fixing the cause of the warning this seems a bit tricky here. The spammed warnings are:

• -Wsign-compare: happens on loop bounds, when the loop bound is taken from lfs.size() with auto. would need some deep digging in the loopy type system.
• -Wunused-variable: happens in code generation when the existence of the variable was detected in one place but it later turned obsolete.
• -Wcpp: Christian spams these from dune-istl

Long story short, I would like to see them ignored. Thoughts?