Fix compilation warnings #2531
Description
O2Physics compilation warnings are not treated as errors by default since #2012 to avoid breaking the CI checks when a new warning is introduced by a compiler. Only explicitly listed warnings make the CI check fail.
If one wants a warning to become an error, all instances have to be fixed first and then the warning can be added in the CMAKE_CXX_FLAGS variable in dependencies/O2PhysicsCompileFlags.cmake.
Currently checked warnings (reference):
-Wunused-variable