Some modules change CMake minimum required version when they are
included. For example:

  cmake_minimum_required(VERSION 2.8.12)
  message("${CMAKE_MINIMUM_REQUIRED_VERSION}")
  include(CheckTypeSize)
  message("${CMAKE_MINIMUM_REQUIRED_VERSION}")

will produce the following output:

  2.8.12
  2.6

This patch ensures that when you include a CMake module the minimum
required version and the policies set are left unchanged.

Fixes Issue #14864