Avoid read barrier in `ArtMethod::IsOverridableByDefaultMethod()`.

Also clean up a few other things related to method linking.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Bug: 181943478
Bug: 119486698
Change-Id: I888dd63db272075cad524e561b3f6271445e8b00
3 files changed