Install PHP ast extension through package

Summary:
FreeBSD devservers can now use php74-pecl-ast, which is well maintained
and kept up-to-date to install this extension.

This is a follow-up for 14ebe96219b5.

Test Plan: Tested on WindRiver

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2363