Currently, libyuv is setting this config via mac_sdk_min_build_override. The old
meechanism is deprecated, but cannot be removed until chromium is updated to no
longer require mac_sdk_min_build_override.

TBR=kjellander@chromium.org
Bug:chromium:740693
Change-Id: I71533c9ef20ac8d7584d50751ac5437da54e2cb5
Reviewed-on: https://chromium-review.googlesource.com/565636Reviewed-by: Frank Barchard <fbarchard@google.com>