use_mangled_mesa() command should not be called.
This command was created in September 2001 to support VTK before modern CMake language and custom command capabilities. VTK has not used it in years.
CMake >= 3.0 prefer that this command never be called. The OLD behavior for this policy is to allow the command to be called. The NEW behavior for this policy is to issue a FATAL_ERROR when the command is called.
This policy was introduced in CMake version 3.0. CMake version 3.6.2 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.
OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.