Hashing FunctionSigs can be quite expensive for large modules;
luckily in some cases we can avoid doing that work.

Change-Id: Ia18060b4c27ab34b44bda4bb81ea05299ecb0f49
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3038523
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75819}