[gdbinit] Slightly increase dcheck stack walk limit

I hit a case where the 'V8_Dcheck' was only the sixth stack frame. Thus
increase the limit from 5 to 7.

R=ahaas@chromium.org

No-Try: true
Change-Id: I1ea37f07ff08ab5acffdfcc89d01ff102750a1e0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2016589
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65943}

tools/gdbinit

@@ -158,7 +158,7 @@ def dcheck_stop_handler(event):
   count = 0
   # limit stack scanning since they're usually shallow and otherwise stack
   # overflows can be very slow.
-  while frame is not None and count < 5:
+  while frame is not None and count < 7:
     count += 1
     if frame.name() == 'V8_Dcheck':
       frame_message = gdb.lookup_symbol('message', frame.block())[0]