In addition to CMAKE_HOST_SYSTEM_PROCESSOR, CMake also defines the CMAKE_SYSTEM_PROCESSOR variable. Whereas the former contains the name of the CPU CMake is currently running on, the latter will contain the name of the CPU we are currently building for. This is a subtle difference that plays a very fundamental role when cross-compiling. We will see more about cross-compilation in Chapter 13, Alternative Generators and Cross-compilation.
An alternative to letting CMake detect the host processor architecture is to use symbols defined within C or C++ and use CMake's try_run function to build and attempt to execute the source code (see Chapter 5, Configure-time and Build-time Operations, Recipe 8, Probing execution) that is branched ...
