https://codereview.chromium.org/2632713003 with workaround for old GCC.

Drive-by: fix unused variable in src/wasm/wasm-js.cc

Bug:chromium:457078

Change-Id: I6c1b65076bae783c31869552bc87d05c28550e26
Reviewed-on: https://chromium-review.googlesource.com/538463
Commit-Queue: Loo Rong Jie <loorongjie@gmail.com>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46049}