Add a simple unwinder for gdb which, on x64,  walks frame pointers
whenever there is no source information available. Ideally we would only
do this for V8 PCs but this appears hard to do in an Unwinder without
messing with gdb's internal assumptions.

Change-Id: Iba1e62a3768340ee912e81d691237c1920a8ae91
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3608628Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80204}