Add a "relaxed" mode for require-artifacts-in-path

This is useful when a makefile will produces different artifacts
depending on other configuration. Having an allow-list that's too strict
can make it a little  difficult to make progress.

Test: m nothing in follow-up
Change-Id: Ic8235912bcbaa8e249a752e042d4f42be4466e34
(cherry picked from commit 0b6fde311ac6bc2b64e69858382117a362645502)