Move CMAKE_HOST_SYSTEM_VERSION detection into cmStateSnapshot.cxx
Can the host system version be reliably extracted from the uname(2)
structure like we do for the os name in 0bbd993f? On Windows we already provide CMAKE_HOST_SYSTEM_VERSION
via the C++ code during EnableLanguage
. That could be moved to the same place we set CMAKE_HOST_SYSTEM_NAME
so that CMAKE_HOST_SYSTEM_VERSION
is available in scripting context, and on all platforms.