A given target offset may already have an environment associated with
it (there can be multiple jumps to the same target). In that case we
used to throw away the previous environment. With this CL we merge the
environments instead.

Bug: v8:7790
Change-Id: I0c22182436fc48e29675e49627729a33cbeaaf4d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1631603
Commit-Queue: Georg Neis <neis@chromium.org>
Auto-Submit: Georg Neis <neis@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61905}