With do-expressions any expression used as a case label can turn into an
OSR entry-point. This means the value being switched over is renamed to
an OSR value and needs to be reloaded from the environment at each case.

R=rossberg@chromium.org
TEST=mjsunit/regress/regress-osr-in-case-label

Review URL: https://codereview.chromium.org/1438123007

Cr-Commit-Position: refs/heads/master@{#31986}