This fixes the label binding mechanism that forwards a label to another
already bound target label. For source labels that are not being reached
by a jump, we should not try to patch jump sites. We still bind the
source label to reflect the target position though, just in case this
binding method will be used for backwards branches in the future.

R=rmcilroy@chromium.org
TEST=webkit/fast/js/parser-syntax-check

Review URL: https://codereview.chromium.org/1804643002

Cr-Commit-Position: refs/heads/master@{#34759}