[Qemu-devel] configure --help lacks explanation of xen-pci-passthrough

[Markus Armbruster]

$ ./configure --help | grep -C 3 xen-pci-passthrough
  virtfs          VirtFS
  mpath           Multipath persistent reservation passthrough
  xen             xen backend driver support
  xen-pci-passthrough
  brlapi          BrlAPI (Braile)
  curl            curl connectivity
  membarrier      membarrier system call (for Linux 4.14+ or Windows)

This is the only --enable thing without an explanation.  Okay, many of
the explanations suck, but that's no excuse.  Xen guys, please provide
one.