janitor: add guards to headers

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/bt.h b/hw/bt.h
index ebf6a37..830af94 100644
--- a/hw/bt.h
+++ b/hw/bt.h
@@ -23,6 +23,9 @@
  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#ifndef HW_BT_H
+#define HW_BT_H 1
+
 #include "hw/irq.h"
 
 /* BD Address */
@@ -2183,3 +2186,5 @@
     SDP_ATTR_NORMALLY_CONNECTABLE		= 0x020d,
     SDP_ATTR_BOOT_DEVICE			= 0x020e,
 };
+
+#endif