Moreover, this is at best an incredibly pedantic point, not something that changes how programmers need to approach UB. You can't review the source code of a compiler that hasn't been written yet.
I'm not suggesting you change how you write code, but with a better implementation the code that you do write - that lives in the real world where mistakes are made - might work better. How is that being pedantic?
An interesting case where compiler writers did something like that is casting via union members, but I'm running out of time, so we can talk about that another day.
Some would prefer less excitement than this.
C code should be more predictable and easier to reason about than using a macro assembler. To the extent it is not, the language has failed.
Perhaps some professional programmers know how to write secure software in a language with undefined behaviour. Maybe we should think about that more rather than just writing off an obviously huge success as a failure?