CMake detect CPU model

CMake can detect the host CPU arch to use with Intel compilers. We discourage package maintainers from settings flags like “-march=native” (GCC, Clang) and “-xHost” (Intel oneAPI) because they may break on user systems such as ARM or HPC. However, the user can set flags for a project by setting environment variables like CFLAGS before the first project configure in CMake. This allows optimizing for a target compiler while compiling from a different host. Or, the user on an appropriate system may simply set their ~/.profile to have CFLAGS=-march=native or similar.