ART: Add marking to thread peer gathering in TI

When CC is marking, we may get stale references due to a missing
mark.

Bug: 34760612
Test: ART_TEST_JIT=true ART_TEST_GC_STRESS=true test-art-host-run-test-924-threads
Test: ART_TEST_JIT=true ART_TEST_GC_STRESS=true test-art-host-run-test-925-threadgroups
Change-Id: I1becfc188b59a3c99cc7eea07c63abaaf108fd15
6 files changed