Symfony version(s) affected: 3.4-dev

Description
PHPUnit Bridge 3.4 claims to be compatible with php 5.3, but after #29903, this is not the case anymore.

How to reproduce
See this Travis build of the Polyfills: https://travis-ci.org/symfony/polyfill/jobs/484968278

Possible Solution
Revert the changes of #29903 at least for the PHPUnit Bridge.