Neon and GCC Intel optimized, but win32 and mips not optimized.

BUG=libyuv:842, b/141482243

Change-Id: Ia56fa85c8cc1db51f374bd0c89b56d21ec94afa7
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/1825642
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Reviewed-by: richard winterton <rrwinterton@gmail.com>