[libvirt] PATCH: Fix build on Mingw32

[Chris Lalancette]

Daniel P. Berrange wrote:
> pread() and pwrite() do not exist on mingw, and the nodedevxml2xmltest
> was adding libvirt_driver_qemu.la for some unknown reason - probably a
> cut & paste error. This broke the test compile when qemu was turned off
> as it is on mingw32.

Might it be better to use gnulib's pread module?  Maybe overkill for this one
case, but it could save us the hassle in the future.

-- 
Chris Lalancette