[NetKVM] Fix buildall.bat so it will clean-up the environment variables after the usage and between compilations of different platforms.
[NetKVM] Fix buildall.bat so it will clean-up the environment variables after the usage and between compilations of different platforms.

virtio-win/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,GoogleCloudPlatform/compute-windows-drivers,vrozenfe/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,ladipro/kvm-guest-drivers-windows,virtio-win/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,GoogleCloudPlatform/compute-windows-drivers,YanVugenfirer/virtio-win-arm,YanVugenfirer/virtio-win-arm,virtio-win/kvm-guest-drivers-windows,GoogleCloudPlatform/compute-windows-drivers,GoogleCloudPlatform/compute-windows-drivers,gnif/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,ladipro/kvm-guest-drivers-windows,gnif/kvm-guest-drivers-windows,daynix/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,YanVugenfirer/virtio-win-arm,virtio-win/kvm-guest-drivers-windows,YanVugenfirer/kvm-guest-drivers-windows,vrozenfe/kvm-guest-drivers-windows