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)
main.mk was a bit cluttered/difficult to follow wth all the indents. Put
the logic in a separate file instead.
Test: m nothing
Change-Id: I545bcd117a6bcd33b520ad279be1bab9b2d89393