The name of the operating system for which CMake is to build.
CMAKE_SYSTEM_VERSION variable for the OS version.
CMAKE_SYSTEM_NAME is not set to anything by default when running
in script mode, since it's not building anything.
System Name for Host Builds¶
CMAKE_SYSTEM_NAME is by default set to the same value as the
CMAKE_HOST_SYSTEM_NAME variable so that the build
targets the host system.