Add phutil-library linter to libphutil

Summary: Ref T2039. See D9070. D9072 is similar.

Test Plan: Ran arc lint.

Reviewers: btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T2039

Differential Revision: https://secure.phabricator.com/D9074