Call willLintPath() hook from PhutilLinter

Summary:
Some callpaths end up here, which doesn't cause the internal linter's willLintPath() method. This can mean its activePath is set wrong, which results in us raising lint for the wrong file.

Particularly, if you apply D7979 (diff 18069) and arc lint it, you'll get a syntax error message in the wrong file.

Test Plan: Applied D7979 and linted it, got proper error message.

Reviewers: btrahan

Reviewed By: btrahan

CC: aarwine, aran

Differential Revision: https://secure.phabricator.com/D7988