It's nonconforming because it's an extension which is also a syntax
error.  If the compiler were warning for that always, it could be
a conforming implementation, but it would be very hard to write conforming
code.  (all it has to do is warn; it is not required to *reject* long long.)

Unless we're using off_t in a stdio function, in which case, our implementation
is really broken.  The list of integral types is exhaustive, at least
for purposes of the standard library.  If any standard library function
is taking or requiring arguments not of standard types, we lose.

(%qd is a legal extension; the code using it is invoking undefined behavior,
but that's ok, it just means the code is only conforming, not strictly
conforming.)

-s