Rather than having GDB always stop on the line containing
V8_IMMEDIATE_CRASH(), walk up the stack looking for V8_Dcheck and select
the frame above it. This will be the frame containing DCHECK (including
related macros like DCHECK_EQ).

Change-Id: I9760e7a4dd78b567dfa77ff12569d287d80ca873
Reviewed-on: https://chromium-review.googlesource.com/1172780Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55112}