Deploy XMLReader PHP extension on FreeBSD

Summary:
The extension isn't provided by base PHP package
and is required by MediaWiki upload feature.

Ref T845.

Test Plan: Upload a file on MediaWiki on Ysul

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T845

Differential Revision: https://devcentral.nasqueron.org/D1455