We currently hit a nullptr access when trying to update the detected
feature set. Instead of adding a check for nullptr there (which would be
unnecessary overhead in production code), we just pass a pointer when
compiling for debugging.

R=thibaudm@chromium.org

Bug: chromium:1092408
Change-Id: I7804edc3f67237bbf28d0ed2f5c58339d3a0f8f7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2238080Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68335}