macro(get_WIN32_WINNT varname_)
    if (CMAKE_SYSTEM_VERSION)
        set(ver ${CMAKE_SYSTEM_VERSION})
        string(REGEX MATCH "^([0-9]+).([0-9])" ver ${ver})
        string(REGEX MATCH "^([0-9]+)" verMajor ${ver})
        # Check for Windows 10, b/c we'll need to convert to hex 'A'.
        if ("${verMajor}" MATCHES "10")
            set(verMajor "A")
            string(REGEX REPLACE "^([0-9]+)" ${verMajor} ver ${ver})
        endif ("${verMajor}" MATCHES "10")
        # Remove all remaining '.' characters.
        string(REPLACE "." "" ver ${ver})
        # Prepend each digit with a zero.
        string(REGEX REPLACE "([0-9A-Z])" "0\\1" ver ${ver})
        set(${varname_} "0x${ver}")
    endif(CMAKE_SYSTEM_VERSION)
endmacro(get_WIN32_WINNT)