GCC fails to compile extract_first_nonzero_index because of the
signedness type mismatch in the NEON intrinsics.

Bug: chromium:819294
Change-Id: I9b73e5fa1d5fbf161740ab1b5d77f5c494369dfa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3693709Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Cr-Commit-Position: refs/heads/main@{#81063}