sim: include ansidecl.h when needed

Avoid implicit include deps with this to help untangle sim headers
so we can get rid of arch-specific sim-main.h.

sim/common/sim-engine.h

@@ -22,6 +22,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <stdarg.h>
 
+#include "ansidecl.h"
+
 typedef struct _sim_engine sim_engine;
 struct _sim_engine
 {