The question is "what would the return value be," and without knowing which compiler is used you don't know what it would return. It doesn't make sense to say the program returns "undefined behavior" or "implementation-dependent."
You might be taking issue with the question itself, but I think it's a valid question because C compilers tend to be lenient with what they compile.
Thing is I can know if the necessary information is provided (i.e. CPU architecture, version of the standard). Portability is a feature of C, but C's portability is mostly syntactic and only partly semantic.
I don't really want to be a pedant here, but in this case if the necessary information was provided, I had the knowledge to find a correct answer. This is different from the case where even if the information was provided I wouldn't be able to know because I don't have the necessary knowledge.
You might be taking issue with the question itself, but I think it's a valid question because C compilers tend to be lenient with what they compile.