raise a SystemError if a function returns a result and raises an exception.
The SystemError is chained to the previous exception.

Refactor also PyObject_Call() and PyCFunction_Call() to make them more readable.

Remove some checks which became useless (duplicate checks).

Change reviewed by Serhiy Storchaka.

Declarations of Windows-specific auxilary functions need Windows types
from windows.h.  Instead of including windows.h in Python.h and making
it available to all Windows users, it is simpler and safer just move
declarations to the single file that needs them.

fstat() may fail with EOVERFLOW on files larger than 2 GB because the file size type is an signed 32-bit integer.