Add libxslt as build requires for mingw RPMs
Add libxslt as build requires for mingw RPMs

The libxslt package is needed since:

  commit 94d2d6429d686c5af95115d09c01f3c6bd5ea7c6
  Author: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>
  Date:   Wed Jul 26 17:40:44 2017 +0100

    docs: make xmllint & xsltproc compulsory

The native RPM had it already, but mingw build was missing it.

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

fabianfreyer/libvirt,libvirt/libvirt,fabianfreyer/libvirt,olafhering/libvirt,jardasgit/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,eskultety/libvirt,crobinso/libvirt,jfehlig/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,nertpinx/libvirt,jfehlig/libvirt,eskultety/libvirt,eskultety/libvirt,libvirt/libvirt,crobinso/libvirt,nertpinx/libvirt,nertpinx/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,zippy2/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,olafhering/libvirt,nertpinx/libvirt,zippy2/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt