Enable Freetype, Webp and XPM support in GD

Summary:
Required by Pixelfed

Ref T1481

Test Plan:
Call the following functions:

• imagefttext()
• imagecreatefromxpm()
• imagewebp()

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1481

Differential Revision: https://devcentral.nasqueron.org/D2019