Increase ninja thread count for Windows builds.

Change-Id: Icc3f3cc144d6d3d2ee467822436df94559d6ff37
Reviewed-on: https://skia-review.googlesource.com/107580
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
13 files changed