Make libphutil utils.php PHP version violations statically analyzable

Summary:
Ref T13249. We actually already have a function_exists() check.

We don't have a constant() check, but the next change will add one.

Test Plan: Ran unit tests. No more lint warnings.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13249

Differential Revision: https://secure.phabricator.com/D20145