exclude _none.cpp in G3 build

Change-Id: Ic744d983ff095b979514fa7d033f72b3edae606d
Reviewed-on: https://skia-review.googlesource.com/8281
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ben Wagner <benjaminwagner@google.com>
1 file changed