We instantiate the JumpTableAssembler in patching mode (i.e. directly on
existing code without an intermittent buffer). In this mode it is not
possible to record reloc information. This makes sure we no longer just
blindly write into the non-existing buffer.

R=clemensh@chromium.org
BUG=v8:8028

Change-Id: I4abb8f06cf819fef608e901c4740263f0cecd08a
Reviewed-on: https://chromium-review.googlesource.com/1166834
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54966}