Call cmake_minimum_required(VERSION 3.16) first

CMake version >= 3.16 comes from Google's Foundational C++ Support
matrix:
https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md

Call cmake_minimum_required() first, followed by project().

These changes fix two warnings from cmake version 3.31.5 and 4.0.1.

Change-Id: I42d51f2764d95e23a45a709986011dc0aafb3cf8
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/6451084
Reviewed-by: Frank Barchard <fbarchard@chromium.org>
Reviewed-by: James Zern <jzern@google.com>
Commit-Queue: Frank Barchard <fbarchard@chromium.org>