Most of the C code I write is C99 code, so it is undefined behavior either way for me (if I care about compilers other than GCC and Clang).

That said, I am going to defer to the GCC developers on this since I do not have time to make sense of all versions of the C standard.

That's fair. In the end, what matters is how C is implemented in practice on the platforms your code targets, not what the C standard says.