Add support for `>=cmake-4.0`

[zyxhere]

Cmake-4 breaks compatibility with projects specifying cmake_minimum_required(VERSION 3.5).
This is the warning when building vp9 with cmake-4

 * CMake 4 detected; building with -DCMAKE_POLICY_VERSION_MINIMUM=3.5
 * This is merely a workaround to avoid CMake Error and *not* a permanent fix;
 * there may be new build or runtime bugs as a result.
 * 
 * An upstreamable patch should take any resulting CMake policy changes
 * into account. See also:
 *   https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html

See-also:
https://fedoraproject.org/wiki/Changes/CMake4.0
https://bugzilla.redhat.com/show_bug.cgi?id=2380809
https://bugzilla.redhat.com/show_bug.cgi?id=2376114
https://bugs.gentoo.org/show_bug.cgi?id=951350
https://bugs.gentoo.org/show_bug.cgi?id=964405