message: CMake: Enable CMP0077 in CMake 3.12+
  This allows overriding MESHOPT_ options from the parent CMakeLists.txt
  when that uses add_subdirectory.
  Also refactor CMake version checks to use NOT LESS - GREATER_EQUAL is
  only available in CMake 3.7+ but NOT LESS should work everywhere and is
  more concise.
diff: cmake_minimum_required(VERSION 3.0)
  -if (CMAKE_VERSION VERSION_GREATER 3.15 OR CMAKE_VERSION VERSION_EQUAL 3.15)
  +if (NOT CMAKE_VERSION VERSION_LESS 3.12)
  + cmake_policy(SET CMP0077 NEW) # Enables override of options from parent CMakeLists.txt
  +endif()
  +
  +if (NOT CMAKE_VERSION VERSION_LESS 3.15)
  cmake_policy(SET CMP0091 NEW) # Enables use of MSVC_RUNTIME_LIBRARY
  cmake_policy(SET CMP0092 NEW) # Enables clean /W4 override for MSVC
  endif()
  