There is a generated file config.descriptor which is an output file
for a particular target. When we try to add this to sources, it breaks
as GN no longer silently accepts files with invalid types as sources.

This breakage was due to recently-rolled changes to fix crbug.com/gn/77

Similar fixes have been used here: crbug.com/964411

Change-Id: Ica9272647c6d1ed31780a6319cf098a083a3cc57
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1674032
Auto-Submit: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62340}