implemented SK_CLOCKWISE_BUILTIN for Metal SkSLC

Bug: skia:
Change-Id: I0b77113868be8e5a719e9a286ecf7f87e5c86367
Reviewed-on: https://skia-review.googlesource.com/146533
Commit-Queue: Timothy Liang <timliang@google.com>
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
1 file changed