build: update node.gyp to reference gypfiles/v8.gyp

Refs: https://github.com/v8/v8/commit/f9934aa9cf77b76c5fa78137e32939f30d9e2f81
Fixes: https://github.com/nodejs/node-v8/issues/36

PR-URL: https://github.com/nodejs/node/pull/19201


Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>