Log Message:
update of expat from 2.2.0 to 2.2.1 (mostly security fixes and cleanup)

Security issues fixed:
CVE-2017-9233, CVE-2016-9063, improve fix for CVE-2016-5300

fixed regression from fix to CVE-2016-0718

Cleanup: Drop AmigaOS 4.x, Borland C++ Builder, OpenVMS, Open Watcom,
Visual Studio 6.0 and Pre-X Mac OS support