Avoid updating class loaders outside system weaks

We update all system weaks using Runtime::SweepSystemWeaks(). But when
we are tracing, we attempt to update them again via
ClassLinker::VisitRoots, which results in double updation of GC-root.
This is not tolerated by userfaultfd-GC as we do in-place sliding
compaction.

Bug: 250480435
Test: art/test/testrunner/testrunner.py --host --gcstres -t
2240-tracing-non-invokable-method

Change-Id: I970f2d47270837f7b02f34d34ae434ba8a4edd2b
1 file changed