Fix the issue involving inconsistent whitespace in BUILD.gn which broke
Node's GN scraper.

Refs: https://github.com/nodejs/node-v8/issues/113
Bug: v8:9579
Change-Id: I5313cd652634b393fb3eab13f0f2bd483a3c6a97
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1734946
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63058}