tests: Add libqemustub to qom-interface-check

The recent addition of util/error.c's dependency on error_report()
causes this test to fail to link due to a number of missing monitor
related symbols. All these symbols are however defined by libqemustub.
Add this libary to the link.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
