Fix false compatibility return status on extension.

Also, don't diff unreferenced anonymous records.

Bug: 64267858
Bug: 72697345

Test: Extend libjpeg by adding an exported function, also add an unused struct;
      Without this change: build shows an 'error' message, but does not fail.
      With this change in prebuilts : build shows 'error' message and
      fails.

Test: tests/test.py passes.

Change-Id: Ief7ed90715a9c1a25736c10449833650c73d3db3