header/intsafe: Fix Cygwin compatibility.

In 64-bit Cygwin, both "long" and "long long" are both 64-bit types,
so some 64-bit types that we assumed were the same are actually different.
- size_t (unsigned long) != UINT_PTR (unsigned long long)
- ptrdiff_t (long) != INT_PTR (long long)

Signed-off-by: LIU Hao <lh_mouse@126.com>