Apex_available check failure reveals dependency

When the check for apex_available has failed, the build system now shows
the module that brought the unavailable module into the APEX.

Bug: 151051671
Test: m
Merged-In: Id1a3fda67fe56fdc2dc90ec800d10689415de4d6
(cherry picked from commit 7bd9444b)
Change-Id: Id1a3fda67fe56fdc2dc90ec800d10689415de4d6