int main() and rule 6.3

[Lundin]

I was wondering whether rule 6.3 applies to int main() or if this is should be a special exception? Ie should we write sint16_t main() or not?
Because if we state the width and signedness of main() we will suddenly make the app implementation-dependant and non-portable.

Also, ISO C strictly states that the return type shall be "int" on a hosted environment. One could interpret that as "it must be the primitive
data type int and no custom typedef".