Install manually phpcs on FreeBSD

Summary:
Provide a more stable workaround for the PHP 5.6 <> PHP 7.1 roulette issue
documented in ff78ba16e3d7 with a more stable workaround.

Test Plan: Test on Ysul (FreeBSD) and Eglide (not FreeBSD, must be no op)

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1319