JNI compiler: Rewrite exception polling.

Make the slow path explicit in the JNI compiler. Fix the
CFI data for the exceptional path of synchronized methods.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: run-gtests.sh
Test: testrunner.py --target --optimizing
Bug: 172332525
Change-Id: If64965eef15c063e36b78dd8bb6cba5af34ab4fa