sim: replace custom attributes with ansidecl.h

A lot of this code predates the common attributes.  We had already
started migrating over piece by piece, so just do a pass across all
the attributes and replace most of them.

sim/m32c/m32c.opc

@@ -22,13 +22,12 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "ansidecl.h"
 #include "cpu.h"
 #include "mem.h"
 #include "misc.h"
 #include "int.h"
 
-#define AU  __attribute__((unused))
-
 #define tprintf if (trace) printf
 
 static unsigned char