Thanks for the quick review.  I considered guarding the include with
#ifdef as well, but I concluded it's not necessary for the following
reasons:

1. a large number of existing tests already simply include <sys/types.h>
(the makedev test, sizeof(off_t) test, IPv6-related tests, and various
socket tests);

2. if sys/types.h doesn't exist, the test will fail, and Python will
conclude that %zd is not available.  This conclusion is almost certainly
correct, as I doubt that a system without sys/types.h has a working %zd
format.