How to determine host architecture before to the project call?

In my project I’m allowing the user to configure library either for device or simulator. When targeting device I just hardcode arm64, but the simulator architecture follow the host device. Unfortunately I cannot use CMAKE_HOST_SYSTEM_PROCESSOR as this choice needs to be made prior the project call to set various variables.

What are my other options?

Answering my own question:

cmake_host_system_information(RESULT _simulator_arch QUERY OS_PLATFORM)

did the trick.