In export wrappers generated code, load the undefined value from the
wasm instance rather than from the isolate. With asynchronous
compilation, the isolate may not be available.

R=mstarzinger@chromium.org

Bug: v8:9554
Change-Id: Ic448bda82c2125fc9c9f8715bce26870308715d2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1722556Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62946}