This was previously undetected due to a now fixed typing bug.

BUG= https://bugs.chromium.org/p/v8/issues/detail?id=4203
TEST=test-asm-validator,asm-wasm
TBR=titzer@chromium.org
LOG=N
NOTRY=true

Review URL: https://codereview.chromium.org/1823333005

Cr-Commit-Position: refs/heads/master@{#35048}