There is not really a reason to guard the first by the latter. Just emit
a hint if --trace-liftoff is used without --trace-wasm-decoder, but
still make it work.
Also, used DEFINE_DEBUG_BOOL instead of guarding the output by another
"#ifdef DEBUG".

R=ahaas@chromium.org

Change-Id: Ia7d3f504df92779447877612e98b9c2a847b9f6b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2011828Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65894}