Use a sentinel when clearing JIT table entries.

This can help diagnosing crashes we see.

bug: 38128052
bug: 37949368
Test: test.py --jit

(cherry picked from commit 6ca115b5fa185a2cc162a453f425efd87d8f38bd)

Change-Id: Ib048f72cef7acfdb15f515c63a2ff0ac8e3744ce
1 file changed