windows: fix support for WIN_SDK < 19041

inspired by :
Since CMake doesn't really has a way of providing the Win10 SDK's version ( see: )
we read the XML file set up by the SDK and filter the SDK version out of it
1 job for master in 4 minutes and 6 seconds (queued for 241 minutes and 15 seconds)
Status Name Job ID Coverage
passed linux kf5-qt5 qt5.15 #112145