How to use CMAKE_SYSTEM_PROCESSOR policy?

There is a discussion in the following link about how CMAKE_SYSTEM_PROCESSOR is restrictive for armclang (it adds --cpu flag which may not be wanted).

https://gitlab.kitware.com/cmake/cmake/-/issues/21173

Apparently the behaviour can now be overridden by a ‘policy’. I’m not familiar with CMake ‘policies’. How would I invoke the relevant policy please?

Sorry, explained here:

CMP0123 — CMake 3.22.2 Documentation

and here:

cmake_policy — CMake 3.20.6 Documentation