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