FILE GLOB_RECURSE calls should not follow symlinks by default.

In CMake 2.6.1 and below, FILE GLOB_RECURSE calls would follow through symlinks, sometimes coming up with unexpectedly large result sets because of symlinks to top level directories that contain hundreds of thousands of files.

This policy determines whether or not to follow symlinks encountered during a FILE GLOB_RECURSE call. The OLD behavior for this policy is to follow the symlinks. The NEW behavior for this policy is not to follow the symlinks by default, but only if FOLLOW_SYMLINKS is given as an additional argument to the FILE command.

This policy was introduced in CMake version 2.6.2. CMake version 3.0.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.