This fixes a race with the aforementioned runtime function where the
global map from Isolate to WasmCompileControls was accessed without
proper synchronization. These are reported by "TSAN isolates".

R=sigurds@chromium.org
TEST=mjsunit/wasm/compilation-limits

Change-Id: Iaeea7f54cbb5051ca0ca97d75543e38ab9f9addc
Reviewed-on: https://chromium-review.googlesource.com/1193243Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55465}