Legacy types can cause build errors with code that defines
them differently.  Disable them by default.  Allow the types
to be enabled with #define LIBYUV_LEGACY_TYPES

BUG=libyuv:808
TESTED=libyuv try bots still build

Change-Id: I48928329393f44a377cec781e645570b14569668
Reviewed-on: https://chromium-review.googlesource.com/1129558
Commit-Queue: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@chromium.org>