qtest: fix vhost-user-test compilation with old GLib

Mising G_TIME_SPAN_SECOND definition breaks the RHEL6 compilation as GLib
version before 2.26 does not have it. In such case just define it.

Reported-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tests/vhost-user-test.c

@@ -22,6 +22,10 @@
 #include <qemu/sockets.h>
 
 /* GLIB version compatibility flags */
+#if !GLIB_CHECK_VERSION(2, 26, 0)
+#define G_TIME_SPAN_SECOND              (G_GINT64_CONSTANT(1000000))
+#endif
+
 #if GLIB_CHECK_VERSION(2, 28, 0)
 #define HAVE_MONOTONIC_TIME
 #endif