If you live in an "all compiler warnings are errors" world, having two compilers where a bit of code can cause a warning in one compiler and not cause a warning in another compiler is really annoying.
You should always strive for zero warnings on all builds across all compilers. It's a realistic, achievable and worthwhile goal. But while pretty much all warnings are worth looking at, a much smaller set are worth breaking the build over. You're much better off (in my view) promoting those particular warnings to errors, and leaving the rest as-is.
If you are an application developer and a compiler X gives warnings that compiler Y doesn't for your application, then ideally you should probably fix the warnings from compiler X. An end user probably doesn't care either way, they just want to compile the program without any issues.