Newer gdb versions require the return type to be specified.

Change-Id: Ia9c160858036e9cbbe1ced123bbcc79d9efb78b4
No-Try: true
No-Presubmit: true
No-Tree-Checks: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2082561Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66554}