Since commit b8a32e0e94d75702714167539310f0df4d268e0f, all man pages
depend on configure.ac so that they are properly regenerated whenever
libvirt version changes. Thus libvirt.spec needs to have a build
dependency on pod2man when %{enable_autotools} is set.
(cherry picked from commit 6f1b9c8d2ab3f28d1b94f6aca0e2695632fa7019)