The version of the operating system for which CMake is to build.
CMAKE_SYSTEM_NAME variable for the OS name.
System Version for Host Builds¶
CMAKE_SYSTEM_NAME variable takes its default value
CMAKE_SYSTEM_VERSION is by default set to the same value as the
CMAKE_HOST_SYSTEM_VERSION variable so that the build targets
the host system version.
In the case of a host build then
CMAKE_SYSTEM_VERSION may be set
explicitly when first configuring a new build tree in order to enable
targeting the build for a different version of the host operating system
than is actually running on the host. This is allowed and not considered
cross compiling so long as the binaries built for the specified OS version
can still run on the host.