Fix issue with RawMonitors around thread suspension.

Investigation of real-world JVMTI agents revealed that some rely on
the RawMonitorEnter function acting as a Java suspend point. If it
fails to act as one the agent could end up deadlocked.

Test: ./test.py --host -j50
Bug: 62821960
Bug: 34415266

Change-Id: I3daf5c49c1c9870e1f69eebfd4c6f2ad15224510