CMP0124

The loop variables created by foreach() command have now their scope restricted to the loop scope.

Starting with CMake 3.21, the foreach() command ensures that the loop variables have their scope restricted to the loop scope.

The OLD behavior for this policy let the loop variables to exist, with an empty value, in the outer scope of loop scope.

This policy was introduced in CMake version 3.21. Use the cmake_policy() command to set it to OLD or NEW explicitly. Unlike many policies, CMake version 3.21.0-rc3 does not warn when the policy is not set and simply uses OLD behavior.