Fix --without-libvirtd builds

When building with --without-libvirtd and udev support is detected we
will fail to build with the following error:
    node_device/node_device_udev.c:1608:37: error: unknown type name
        'virStateInhibitCallback'

src/Makefile.am

@@ -1238,6 +1238,7 @@ libvirt_driver_nodedev_la_CFLAGS = \
 libvirt_driver_nodedev_la_LDFLAGS = $(AM_LDFLAGS)
 libvirt_driver_nodedev_la_LIBADD =
 
+if WITH_LIBVIRTD
 if WITH_HAL
 libvirt_driver_nodedev_la_SOURCES += $(NODE_DEVICE_DRIVER_HAL_SOURCES)
 libvirt_driver_nodedev_la_CFLAGS += $(HAL_CFLAGS)
@@ -1248,6 +1249,7 @@ libvirt_driver_nodedev_la_SOURCES += $(NODE_DEVICE_DRIVER_UDEV_SOURCES)
 libvirt_driver_nodedev_la_CFLAGS += $(UDEV_CFLAGS) $(PCIACCESS_CFLAGS)
 libvirt_driver_nodedev_la_LIBADD += $(UDEV_LIBS) $(PCIACCESS_LIBS)
 endif
+endif
 
 if WITH_DRIVER_MODULES
 libvirt_driver_nodedev_la_LIBADD += ../gnulib/lib/libgnu.la