Newer CMake causes issues with legacy FindBoost module

[rbberger]

With current CMake versions you get:

CMake Warning (dev) at ......./lib64/cmake/HPX/HPX_SetupBoost.cmake:134 (find_package):                                                
  Policy CMP0167 is not set: The FindBoost module is removed.  Run "cmake
  --help-policy CMP0167" for policy details.  Use the cmake_policy command to
  set the policy and suppress this warning.

Building other projects like FleCSI which use the Boost Config module and this logic can create conflicts. Please migrate to the Boost provided Config module.

[Pansysk75]

Thank you for opening this issue. PR #6510 should fix this and will be merged soon.