The libexpat 2.4.1 upgrade from introduced the following new exported symbols:
* `testingAccountingGetCountBytesDirect`
* `testingAccountingGetCountBytesIndirect`
* `unsignedCharToPrintable`
* `XML_SetBillionLaughsAttackProtectionActivationThreshold`
* `XML_SetBillionLaughsAttackProtectionMaximumAmplification`
We need to adjust [Modules/expat/pyexpatns.h](https://github.com/python/cpython/blob/master/Modules/expat/pyexpatns.h)
(The newer libexpat upgrade has no new symbols).
Automerge-Triggered-By: GH:gpshead