spec: collect all BuildRequires into one area

Conditional BuildRequires: should be at the top level, rather
than appearing in conditional sub-package sections.  This
appears to be the only offender.

* libvirt.spec.in (BuildRequires): Move libblkid-devel into
correct area.
Signed-off-by: NEric Blake <eblake@redhat.com>

libvirt.spec.in

@@ -412,6 +412,10 @@ BuildRequires: gettext
 BuildRequires: libtasn1-devel
 BuildRequires: gnutls-devel
 BuildRequires: libattr-devel
+%if %{with_libvirtd}
+# For pool-build probing for existing pools
+BuildRequires: libblkid-devel >= 2.17
+%endif
 %if 0%{?fedora} >= 12 || 0%{?rhel} >= 6
 # for augparse, optionally used in testing
 BuildRequires: augeas
@@ -655,8 +659,6 @@ Requires: PolicyKit >= 0.6
 Requires: nfs-utils
 # For mkfs
 Requires: util-linux
-# For pool-build probing for existing pools
-BuildRequires: libblkid-devel >= 2.17
 # For glusterfs
         %if 0%{?fedora} >= 11
 Requires: glusterfs-client >= 2.0.1