Fix the parameter and return types for longobject in cpyext on win64, fixing lib-python
cpyext.test.test_longobject with a corrected value on win64.
Also fix parameters in
PyBuffer_FillInfo, since Signed doesn't make sense as a parameter type in cpyext.
The only other occurrence of Signed I can see in cpyext function signatures are the hash functions, and it is OK there (CPython typedefs Py_hash_t as Py_ssize_t which is the same as Signed).
numpy.test('full') on this PR on win64 now returns only 8 fails/errors (most of which look related to PyPy's GC, not win64).