Issue #17106: Fix a segmentation fault in io.TextIOWrapper when an underlying
stream or a decoder produces data of an unexpected type (i.e. when
io.TextIOWrapper initialized with text stream or use bytes-to-bytes codec).
Update the embedded copy of the expat XML parser to 2.1.0.  It brings
with it a vareity of bug fixes, both security and behavior.  See
http://www.libexpat.org/ for the list.

NOTE: I already backported the expat hash randomization fix in March.

Fixes issue #14340.
Issue #6083: Fix multiple segmentation faults occured when PyArg_ParseTuple
parses nested mutating sequence.
Temporarily disable test_from_dll in test_returnfuncptrs.py for Windows.
Do not raise self.skipTest().
skipTest() already raises an exception.