When --single-threaded is set, and therefore
--wasm-num-compilation-tasks=0, the compilation job for JSToWasm
wrapper compilation is executed directly instead of first posted and
then joined on the main thread.

R=clemensb@chromium.org

Bug: v8:11279
Change-Id: Idba150cf9d32a6a6b12b322f46c0ba36fd220c5b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2595441
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71953}