Currently it's possible to hit an internal compiler error by declaring a
non-extern class that doesn't extend anything. It's not very meanigful
for a class to not extend from anything, so the parser should enforce
this requirement.

Change-Id: I38064f87345d28ce84521261bbfd33d9b1c71334
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2153847
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67212}