--trace-wasm-decoder should not imply --single-threaded, as
--single-threaded implies --no-liftoff. Hence we cannot trace the
decoder in Liftoff mode.

R=thibaudm@chromium.org

Change-Id: I3e4f0ea119288ef88c4b00dd2f2a11244b77c204
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2287492Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68741}