""code can be result of macro expansion"

Might be wrong but the big issue with warning about UB probably isn't C it's C++ and it's templates. Modern C is mostly what you see is all there is. Where with C++ lord knows really.

C is often a bit slower than C++. Which also means trading a little speed to eliminate UB isn't a big hit. Where doing that inside a template expansion can slow things down a lot.

My preferred solution is people stop using C++.