Comment 2 for bug 120292

It seems to be as straightforward as:
apt-get build-dep qemu
apt-get --compile source qemu

Plus (if you want to do things properly) filling-in the changelog and changing vde2 to vde2|vde in the dependencies (since vde2 isn't available in feisty). I don't have much time but I'll try to experiment a bit to check if other related packages also need to be recompiled.